Abundance of small cetaceans in waters of the central Spanish Mediterranean

Seasonal aerial surveys were conducted in the waters of the central Spanish Mediterranean from 2001 to 2003 using the line transect sampling methodology to estimate cetacean abundance. The density of the three most abundant species, striped dolphin (Stenella coeruleoalba), bottlenose dolphin (Tursiops truncatus) and Risso’s dolphins (Grampus griseus), was estimated. In the case of the first two species, the density was estimated accounting for the proportion of submerged animals, while for Risso’s dolphin only the surface density could be estimated. The striped dolphin was the most abundant species in the study area with a mean density of 0.489 dolphins km⁻² (95% CI = 0.339–0.705) and a mean abundance of 15,778 dolphins (95% CI = 10,940–22,756). This density is comparable to that obtained in the International Ligurian Sea Cetacean Sanctuary. Striped dolphins were observed throughout the whole year and no seasonal changes in the density were detected. The mean density of bottlenose dolphins was an order of magnitude lower than that of striped dolphins (0.041 dolphins km⁻²; 95% CI = 0.023–0.075) with a mean abundance of 1,333 dolphins (95% CI = 739–2,407). The Risso’s dolphin had a surface estimated density of 0.015 dolphins km⁻² (95% CI = 0.005–0.046) and a mean abundance of 493 dolphins (95% CI = 162–1,498). These results provide valuable biological information useful to develop conservation plans and establish a baseline for future population trend studies.     

Temporal variation of Tubularia indivisa (Cnidaria, Tubulariidae) and associated epizoites on artificial habitat communities in the North Sea

We have analyzed the composition, diversity, density and biomass of a temporal series of samples taken in a Tubularia indivisa community, which dominates a shipwreck in the North Sea waters (N 51°23′,730–E 02°29′,790, 17 nautical miles from the coast, 30 m depth). This shipwreck has structures emerging up to 8 m above the seabed. Water temperature ranged from 4.2°C in March to 20.3°C in August. Salinity showed few variations around 33.9 psu. Bottom tidal currents followed a semi-diurnal cycle and were preferentially NE oriented with 84% of them in the range 0.25–0.75 m s⁻¹. The mean value for total suspended matter was 6.2 mg l⁻¹ with large variations on a monthly scale. The species richness of samples varied from 15 in October to 42 in August with a mean value of 33 species. Diversity indices were higher during autumn and winter because of the strong dominance of a few crustacean species during the warmer months. The total density of individuals ranged from 6,500 ind m⁻² in October to 445,800 ind m⁻² in July, most of these individuals belonging to the amphipod species Jassa herdmani. The biomass of the T. indivisa community varied from 9 g AFDW m⁻² in October to 1,106 g AFDW m⁻² in July, with T. indivisa itself constituting between 59 and 82% of the total biomass. The biomass of T. indivisa was positively correlated with species richness and with the density of 23% of the species identified on this community, suggesting that T. indivisa plays an important structural role in this habitat. This was further confirmed by the number of species associated with T. indivisa which was generally superior to 55% of the sorted species. Multivariate analysis indicated strong differences between spring/summer−autumn/winter assemblages mostly but not solely due to the abundance patterns of species. These findings support the conclusion that shipwrecks in Belgian waters allow the development of assemblages dominated by a high biomass of T. indivisa which in turn provides shelter for high densities and biomass of epizoites. These assemblages will further show large monthly variations in densities and composition due to large variation in T. indivisa biomass under an apparent repetitive annual cycle. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seasonal vertical distribution and population dynamics of the chaetognath Parasagitta elegans in the water column and hyperbenthic zone of Conception Bay, Newfoundland

The vertical distribution and population dynamics of the chaetognath Parasagitta elegans Verrill were determined in the water column and hyperbenthic zone of Conception Bay, Newfoundland from April 1997 to June 1998. The water column depth at the study site (47°32.2′N; 53°07.9′W) was 235 m. The temperature below the thermocline was <0 °C the year round. Chaetognath samples from the water column were collected with a Tucker Trawl. Those from the hyperbenthic zone, were collected with an epibenthic sledge. Depending upon whether the hyperbenthic zone was assumed to extend either 1 m or 10 m above bottom, the grand mean, areal abundance of chaetognaths in the hyperbenthic zone ranged from 6% to 40% of the total abundance in the water column (including the hyperbenthic zone), and the grand mean, areal biomass ranged from 25% to 77%. Large, mature individuals were collected only in the hyperbenthic zone, whereas small, immature individuals were collected primarily in the water column. According to body length and ovary maturity data, three cohorts were identified in the hyperbenthic zone during the study period. Within each cohort, the length frequency of reproductively mature individuals was bimodal, with groups of mean length 33 mm and 41 mm reproducing from May to October. The recruitment period of juvenile chaetognaths extended from July to February, coinciding with the recruitment period of copepods. The estimated individual growth rate of P. elegans was 1.0 mg C year⁻¹. The approximate generation time of the two groups of individuals with mean length at maturity of 33 mm and 41 mm was 450 and 780 days, respectively. This study demonstrates that a failure to sample the large, mature P. elegans living in the hyperbenthic zone leads to serious underestimates of the total abundance and biomass of chaetognaths and an inaccurate picture of seasonal population dynamics. Received: 8 September 1999 / Accepted: 15 September 2000     

Habitat modification affects recruitment of abalone in central New Zealand

The habitat experienced during early life-history stages can determine the number and quality of individuals that recruit to adult populations. In a field experiment, biogenic habitat complexity was manipulated (presence or absence of foliose macroalgae) at two depths (2–3 m and 5–6 m) and the habitat-dependent effects on recruitment of the black foot abalone (Haliotis iris) were examined at three field sites along the south coast of Wellington, New Zealand (41°20′S, 174°47′E), between July and November 2005. Recruit density (<5 weeks post-settlement) was measured on cobbles covered with crustose coralline algae. Habitats of low complexity (barrens treatments) had consistently greater densities of recruits than habitats of high complexity (algae treatments). However, recruits in algae habitats were larger, and for deep habitats, there was greater survival in algae habitats compared with barrens habitats. While depth had no significant effect on early recruit (<2 weeks post-settlement) density, late recruit (<5 weeks post-settlement) density was greater in shallow habitats, and so it seems recruit survival was greater in shallow habitats. In this experiment, algal habitat complexity had strong effects on early recruit abundance, but habitat-dependent variations in recruit growth and survival may modify initial patterns of abundance and determine recruitment to adult abalone populations.     

Patterns of time and space utilisation in coelacanths (Latimeria chalumnae), determined by ultrasonic telemetry

Acoustic telemetry was used to examine patterns of activity and space utilisation of coelacanths, nocturnal predators which spend the day in submarine caves. Nine coelacanths (Latimeria chalumnae) were tracked, each for a period of 1 to 16 nights at Grande Comore, West Indian Ocean. Activities lasted on average 9 h, usually starting shortly after sunset and ending before sunrise. Vertically, coelacanths moved up and down at and below cave level by following the bottom contour, mainly between 180 and 400 m depth. The deepest record was 698 m, the shallowest 133 m. Most time was spent between 200 and 300 m depth. Large individuals performed deep excursions to depths below 400 m, usually once per night. The fish spent most time in water temperatures of 15 to 19 °C; they rarely ventured into waters warmer than 22 °C measured at depths shallower than 160 m depth. Horizontally, coelacanths stayed in narrow areas ranging from <1 to 10 km of coastline. Coelacanths are extremely slow drift-hunters with an estimated average swimming speed of 3.2 m min⁻¹, often travelling not more than 3 km per night. They probably take advantage of local upwelling and downwelling and slow currents occurring parallel to the steep slopes. This study shows that coelacanths are inhabitants of the subphotic zone, where they are active mainly below the depth of their daytime refuges. Received: 7 July 1999 / Accepted: 11 February 2000     

Migration,distribution, and diving behavior of adult male loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) following dispersal from a major breeding aggregation in the Western North Atlantic

Sixteen satellite-tagged adult male loggerhead sea turtles (Caretta caretta) dispersed widely from an aggregation near Port Canaveral, Florida, USA (28°23′N, −80°32′W) after breeding. Northbound males migrated further (990 ± 303 km) than southbound males (577 ± 168 km) and transited more rapidly (median initial dive duration = 6 (IQR = 4–16) versus 19 (IQR = 10–31) min, respectively).. Migration occurred along a depth corridor (20–40 m) except where constricted by a narrow continental shelf width. Males foraged in areas 27 ± 41 km² day⁻¹ at locations <1–80 km from shore for 100.1 ± 60.6 days, with variability in foraging patterns not explained by turtle size or geography. Post-breeding dispersal patterns were similar to patterns reported for adult female loggerhead sea turtles in this region and adult male loggerhead sea turtles elsewhere in the northern hemisphere; however, foraging ground distributions were most similar to adult female loggerhead sea turtles in this region.     

Physiological tolerance predicts species composition at different scales in a barnacle guild

This study examined how the species composition of an intertidal barnacle guild varied according to physical gradients in the environment at small scales governed by microclimates, medium scales of wave exposure and large scales of latitude. Barnacle distributions at small and medium scales were sampled in Ireland between 51°29′ and 52°44′N and 6°50′ and 10°08′W. Sampling on European shores spanned ~18° latitude from 37°05′ to 55°16′N. Barnacle surveys mainly took place in 2003–2004. An index of wave fetch was calculated along the wave exposure gradient using a digital coastline-based model that was supported by a biological exposure scale. A ‘dryness’ index was defined according to mean monthly wind speed, fetch along the average wind direction and mean monthly air or sea surface temperatures for 2 years (January 2001–December 2002) which is the period when the most recent adults in the barnacle community would have settled and grown to adulthood. The proportion of the dry-loving barnacle Chthamalus montagui Southward increased within the barnacle guild at all scales as the habitat became warmer and drier. Barnacle densities were high in all habitats, mean densities ranged from a minimum of 4.16 cm⁻² on moderately exposed shores to a maximum of 6.27 cm⁻² in sunlit or south-facing microclimates. Percentage cover of barnacles across the gradient of latitudes was usually >70%. The results suggest that the distribution and abundance of interacting barnacle species on European coasts is strongly controlled by abiotic factors, most likely temperature and desiccation.     

Emergence of an oocytic circumnuclear ring in response to increasing day length in Atlantic herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

Understanding physiological and environmental variables that initiate sexual maturity would provide fundamental information on life history dynamics. The aim of this study was to test the usefulness of the common circumnuclear ring (CNR), an oocytic structure similar to the Balbiani body, which appears just prior to oocyte development as a predictor of first maturation in Atlantic herring (Clupea harengus). The relative roles of physiology (e.g. fat) and photoperiod as triggers of maturation were also investigated. Samples were collected in May 2008 (72°26′–73°84′N/11°26′–18°40′E) and February 2009 (56°12′–59°45′N/00°25′–03°06′W). These data suggested that thresholds in body size may influence the decision to mature. We also found that short days (winter solstice) may be the photoperiod trigger for a first-decision window for both Norwegian spring-spawning (NSS) and North Sea autumn-spawning (NSAS) herring. The second-decision window for NSAS herring maturation appears to be triggered by longer days (spring equinox), while a decreasing rate of day lengthening may trigger NSS herring maturation. So, photoperiodic cycle is a key determinate of the timing of maturation in Atlantic herring.     

Tracking hawksbill sea turtles (<Emphasis Type="Italic">Eretmochelys imbricata</Emphasis>) during inter-nesting intervals around Barbados

Hawksbill sea turtles (Eretmochelys imbricata) nesting in Barbados (Needham’s Point, 13° 04′ 41.33′′ N, 59° 36′ 32.69′′W) were outfitted with GPS dataloggers over three breeding seasons (2008–2010) to track movement during inter-nesting intervals. Most females established spatially restricted resident areas up current and within 7 km of the nesting beach where they spent the majority of the inter-nesting interval. Females nesting earlier in the season settled on shallower sites. Only experienced remigrant turtles occupied the most distant resident areas. Females tracked for multiple inter-nesting intervals exhibited site fidelity, but the area contracted and the activity of females decreased with each successive interval. Hawksbills may trade off site characteristics with distance from the nesting beach and reduce activity over the course of the breeding season to optimise energy reserves during inter-nesting intervals.     

Preliminary patterns of distribution and abundance of loggerhead sea turtles,<Emphasis Type="Italic"> Caretta caretta</Emphasis>, around Columbretes Islands Marine Reserve,Spanish Mediterranean

Aerial surveys were conducted to estimate the abundance and distribution of loggerhead turtles (Caretta caretta) in the Columbretes Islands Marine Reserve and surrounding waters (western Mediterranean). Four surveys were carried out during 2000 and 2001, following the line transect methodology. Loggerheads appeared to be present at high densities in the area throughout the whole year, although density varied between seasons, being more abundant during the spring. Mean density in the study area was 0.322 turtles/km² (range 0.200–0.516) and the mean abundance was 1,324 turtles (range 825–2,124). The turtles were distributed homogeneously throughout the study area, we found no difference in loggerhead density between the water around the reserve and that in the rest of the study area. Current conservation measures planned by the local authorities, which include increasing the area of the reserve, would be very positive for the conservation of this stock.Communicated by S.A. Poulet, Roscoff     

Growth of the scyllarid lobsters Ibacus peronii and I. chacei

The growth rates of the morphologically similar scyllarid lobsters Ibacus peronii (Leach, 1815) and I. chacei (Brown and Holthuis, 1998) are described using data from a tag/recapture study and from tagged lobsters kept in captivity. Within particular size classes, we found no differences in moult increments between male and female I. peronii nor between male and female I. chacei. Small individuals of both species always had larger moult increments than larger individuals. For I. peronii, females moulted more frequently than males, and smaller size classes moulted more frequently than larger size classes. Female I. peronii therefore grew more quickly than males and reached their estimated size at sexual maturity (51 mm carapace length) after ∼2 yr. Moulting of I. peronii was seasonal, with most lobsters (96.3%) moulting between October and January. We found no differences in growth rates of I. peronii at two locations along the east coast of Australia: Coffs Harbour in New South Wales (30°18′S; 153°08′E), and Lakes Entrance in Victoria (37°53′S; 148°00′E). For I. chacei, we found no differences in the frequency of moulting between males and females and, because we also found no differences in the moult increments between males and females, the growth rates of both sexes were the same. Received: 14 August 1999 / Accepted: 20 January 2000     

Life on glass houses: sponge stalk communities in the deep sea

Photographs of the deep-sea floor often show organisms attached to biogenic structures that protrude from the soft bottom. In particular, the stalks of glass sponges (hexactinellids) provide hard substrata and act as habitat islands for deep-sea fauna. The primary objectives of this study were to determine the abundance of glass sponge “stalks” at an abyssal station in the NE Pacific, to identify the fauna associated with stalks, and to compare the distribution patterns of epifaunal taxa both horizontally and vertically. Densities of stalks and large epifauna were estimated from analysis of ∼9 km of photographic transects taken in 1994–1995 at station M (34°45′N; 123°00′W; 4,100 m depth) off California, USA. At least 87% of the stalks were the spicule columns of live or dead hexactinellids in the genus Hyalonema (Gray, 1832). Stalks appeared to be distributed randomly across the sea floor (density: 0.13 stalks m⁻²). A colonial zoanthid, Epizoanthus stellaris (Hertwig, 1888), inhabited 20% of the stalks and was the most commonly observed epifaunal organism, followed by other suspension feeders that generally were situated at the top of the structures. Thirty-five stalk communities were collected in tube cores in 1994–1995 using the submersible “Alvin”. A total of 139 taxa was associated with these hard-substratum habitats (another five species were observed only in photographs). Although taxon richness was high, the species diversity of these communities was relatively low due to the dominance in percentage abundance of a foraminiferan, Cibicides lobatulus (Walker and Jakob, 1798), and a serpulid polychaete, Bathyvermilia sp. (Zibrowius, 1973). The relationship between number of taxa and surface area of the stalks yielded a slope (z-value) typical of islands with a low rate of immigration. Three-dimensional complexity created by branching epifauna on the stalks provided more surface area and a variety of cryptic microhabitats. Vertical zonation on the stalks appeared to be controlled by biological interactions among species, with solitary fauna and certain functional groups of colonial organisms restricted by sheet-like colonial organisms that appeared to be dominant space competitors. Received: 13 April 2000 / Accepted: 9 November 2000     

Phytoplankton production patterns in Massachusetts Bay and the absence of the 1998 winter–spring bloom

The seasonal productivity cycle and factors controlling annual variation in the timing and magnitude of the winter–spring bloom were examined for several locations (range: 42°20.35′–42°26.63′N; 70°44.19′–70°56.52′W) in Boston Harbor and Massachusetts Bay, USA, from 1995 to 1999, and compared with earlier published data (1992–1994). Primary productivity (mg C m⁻² day⁻¹) in Massachusetts Bay from 1995 to 1999 was generally characterized by a well-developed winter–spring bloom of several weeks duration, high but variable production during the summer, and a prominent fall bloom. The bulk of production (mg C m⁻³ day⁻¹) typically occurred in the upper 15 m of the water column. At a nearby Boston Harbor station a gradual pattern of increasing areal production from winter through summer was more typical, with the bulk of production restricted to the upper 5 m. Annual productivity in Massachusetts Bay and Boston Harbor ranged from a low of 160 g C m⁻² year⁻¹ to a high of 787 g C m⁻² year⁻¹ from 1992 to 1999. Mean annual productivity was higher (mean=525 g C m⁻² year⁻¹) and more variable near the harbor entrance than in western Massachusetts Bay. At the harbor station productivity varied more than 3.5-fold (CV=40%) over an 8 year sampling period. Average annual productivity (305–419 g C m⁻² year⁻¹) and variability around the means (CV=25–27%) were lower at both the outer nearfield and central nearfield regions of Massachusetts Bay. Annual productivity in 1998 was unusually low at all three sites (<220 g C m⁻² year⁻¹) due to the absence of a winter–spring phytoplankton bloom. Potential factors influencing the occurrence of a spring bloom were investigated. Incident irradiance during the winter–spring period was not significantly different (P > 0.05) among years (1995–1999). The mean photic depth during the bloom period was significantly deeper (P < 0.05) in 1998, signifying greater light availability with depth. Nutrients were also in abundance during the winter–spring of 1998 with stratified conditions not observed until May. In general, the magnitude of the winter–spring bloom in Massachusetts Bay from 1995 to 1999 was significantly correlated with winter water temperature (r ²=0.78) and zooplankton abundance (r ²=0.74) over the bloom period (typically February–April). The absence of the 1998 bloom was associated with higher than average water temperature and elevated levels of zooplankton abundance just prior to, and during, the peak winter–spring bloom period. Received: 3 July 2000 / Accepted: 6 December 2000     

Impacts associated with the recent range shift of the aeolid nudibranch <Emphasis Type="Italic">Phidiana hiltoni</Emphasis> (Mollusca,Opisthobranchia) in California

In 1977, Phidiana hiltoni (O’Donoghue in J. Entomol Zool (Pomona College, Claremont, California) 19:77–119, 1927) began spreading northward from Monterey, California. By 1992, it had reached Duxbury Reef (37° 53′ 23″ N, 122° 41′ 59″ W), 100 km to the north, where other nudibranchs subsequently appeared to decline. The role of P. hiltoni in this decline was investigated through diet analysis, feeding trials, and comparison of historical and recent abundance data. In the wild, P. hiltoni preyed largely on hydroids, but also showed evidence of predation on nudibranchs. In the laboratory, P. hiltoni attacked most of the dendronotid and aeolid nudibranchs presented to it, ingesting small individuals whole. The pooled abundance of nudibranchs vulnerable to attack by P. hiltoni declined an average of two-thirds at Duxbury Reef since its arrival, compared to (1) no change in the non-vulnerable species and (2) no change in either group at two other sites where P. hiltoni was one to two orders of magnitude less abundant. Phidiana hiltoni therefore appears to have caused this decline, likely through a combination of direct predation and competition for prey. A brief larval period, combined with cyclonic re-circulation in the lee of Point Reyes, may be driving self-recruitment of P. hiltoni at Duxbury Reef, as well as hindering further northward spread.     

A multi-locus genetic assignment technique to assess sources of <Emphasis Type="Italic">Agaricia agaricites</Emphasis> larvae on coral reefs

Assignment of individuals to populations based upon genetic data is an important ecological problem that requires many polymorphic markers, often more than are available using single locus techniques. To demonstrate the utility of amplified fragment length polymorphisms (AFLP) in studying larval dispersal and recruitment in coral populations, two sets of AFLP primers were used to genotype colonies of the coral Agaricia agaricites Linnaeus from three widely separated geographic locations: the Bahamas (23°28′N, 75°42′W) and Key Largo, Florida (24°55′N, 80°31′W—two sites separated by 12 km) in 1995, and the Flower Garden Banks (FGB) in the Gulf of Mexico (27°55′N,93°36′W) in 1997. In addition to adult samples from each site, recruits were collected from settling plates placed on the East FGB for 1 year (1997–1998). The AFLP technique yielded 45 polymorphic markers. An analysis of molecular variance (AMOVA) showed significant genetic differences among the four adult populations, even between the two Key Largo sites. The recruits were significantly different from all adult populations except those from the FGB. Discriminant function analysis and the program AFLPOP were used to assign individuals to populations. Using the adult AFLP-banding patterns to build the statistical models, both procedures correctly assigned the majority of adults to their respective populations in simulations and assigned all but one of the recruits to the Flower Garden population from where they were collected . The AFLP technique provides a simple and adaptable population assignment method for studying recruitment processes in A. agaricites and other coral species. Electronic Supplementary Material Supplementary material is available for this article at     

The role of fungi in processing marine organic matter in the upwelling ecosystem off Chile

In a study that spanned from March 2007 through November 2009, we report high fungal biomass and over 90% of extracellular enzymatic activity occurring in the size classes dominated by fungi during periods of high autotrophic biomass in surface waters of the upwelling ecosystem off central-southern Chile (36°30.80′S–73°07.70′W). Fungal biomass in the water column was determined by the abundance of hyphae and was positively correlated with the concentration of the fungal biomarker 18:2ω6. High fungal biomass during active upwelling periods was comparable to that of prokaryotes (bacteria plus archaea) and was associated with an increase in phytoplankton biomass and in extracellular enzymatic hydrolysis in waters from the depth of maximum fluorescence. We show fungi as a new microbial component in the coastal upwelling ecosystem of the Humboldt Current System off central Chile. Our results suggest that the temporal pattern in fungal biomass in the water column during a year cycle is a reflection of their capacity to hydrolyze organic polymers and, in consequence, fungal biomass and activity respond to a seasonal cycle of upwelling in this ecosystem.     

Distribution and trophic links of gelatinous zooplankton on Dogger Bank,North Sea

The ecology of small, gelatinous zooplankton is not integrated into management of Dogger Bank (54° 00′ N, 3° 25′ E to 55° 35′ N, 2° 20′ E). In pursuit of this goal, gelatinous zooplankton and their potential prey were sampled along a transect across the bank on June 10–16, 2007. Eleven species of small medusae and ctenophores were collected, with six abundant taxa occurring in greater numbers below the thermocline and in the shallower, southeastern portion of the bank. There were no statistically significant diel changes in distribution. In contrast, potential prey were distributed more evenly across the bank and throughout the water column. Isotopic analyses revealed that gelatinous zooplankton fed on both smaller (100–300 μm) and larger (>300 μm) mesozooplankton, but also potentially on each other. These ecological insights suggest that small medusae and ctenophores should be integrated into sustainable management of Dogger Bank.     

Can marine mammals be used to monitor oceanographic conditions?

The breeding performance of higher predators has often been used to monitor fluctuations in the abundance of important prey stocks in marine ecosystems. The development of electronic data-loggers in recent years has also provided the opportunity of using wide-ranging marine animals to measure physical oceanographic conditions. In this study, time–depth recorders (TDRs) programmed to record temperature were deployed on female Antarctic fur seals (Arctocephalus gazella) at Bird Island, South Georgia (54°00′S; 38°02′W) during the breeding seasons 1994 to 1998. Temperature sensors had relatively slow response times, and thermal radiation errors occurred during the day when seals spent a large proportion of their time at the surface. Nevertheless, measurements provided temperature–depth profiles which were typical of the vertical stratification of the ocean. During the early stages of a foraging trip temperature increased, suggesting that fur seals travelled northwards from South Georgia towards the warmer waters of the Polar Front. In addition, higher temperatures were recorded by females that remained at sea for longer, implying that these individuals also travelled further. Mean sea-surface temperature (SST) increased from ∼1 to 4 °C from December to March and agreed with SSTs from ship, buoy and satellite. Future studies on marine mammals which combine satellite tracking with oceanographic measurements are likely to provide valuable information on biophysical aspects of the ocean. Received: 16 June 1998 / Accepted: 13 February 1999     

Tiger shark (Galeocerdo cuvier) abundance and growth in a subtropical embayment: evidence from 7 years of standardized fishing effort

The tiger shark (Galeocerdo cuvier Peron and Lesueur 1822) is a widely distributed predator with a broad diet and the potential to affect marine community structure, yet information on local patterns of abundance for this species is lacking. Tiger shark catch data were gathered over 7 years of tag and release research fishing (1991–2000, 2002–2004) in Shark Bay, Western Australia (25°45′S, 113°44′E). Sharks were caught using drumlines deployed in six permanent zones (~3 km² in area). Fishing effort was standardized across days and months, and catch rates on hooks were expressed as the number of sharks caught h⁻¹. A total of 449 individual tiger sharks was captured; 29 were recaptured. Tiger shark catch rate showed seasonal periodicity, being higher during the warm season (Sep–May) than during the cold season (Jun–Aug), and was marked by inter-annual variability. The most striking feature of the catch data was a consistent pattern of slow, continuous variation within each year from a peak during the height of the warm season (February) to a trough in the cold season (July). Annual growth rates of recaptured individuals were generally consistent with estimates from other regions, but exceeded those for populations elsewhere for sharks >275 cm fork length (FL), perhaps because mature sharks in the study area rely heavily on large prey. The data suggest that (1) the threat of predation faced by animals consumed by tiger sharks fluctuates dramatically within and between years, and (2) efforts to monitor large shark abundance should be extensive enough to detect inter-annual variation and sufficiently intensive to account for intra-annual trends.     

Seasonal distribution patterns of juvenile loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) following capture from a shipping channel in the Northwest Atlantic Ocean

Thirty-four juvenile loggerhead sea turtles captured by trawling from the Charleston, South Carolina (USA), shipping channel (32°42′N; −79°47′W) between May 2004 and August 2007 were tagged with satellite transmitters to assess the extent to which they remained near the capture location given their collection along a seasonal migratory corridor. Seventy-five percent of juveniles were classified as seasonal residents. Migrants predominantly swam north in the spring and nomads wandered south in the summer, but predictive indicators for non-resident status were not identified. All but one juvenile generally remained south of 34°N, within 40 km of shore, and in waters <30 m deep throughout the year. Nine of 14 loggerhead sea turtles monitored during the winter remained exclusively over the continental shelf, three briefly occurred in oceanic habitats, and two foraged extensively in oceanic habitats. Residents distributed >15 km from shore between spring and autumn were three times as likely to occur in oceanic habitats in winter. Modest seasonal movements contrasted with adults tagged at similar latitudes and with juveniles tagged further north and suggest distinct foraging groups within a regional foraging ground.