Mitochondrial DNA analysis of harbour porpoises (Phocoena phocoena) in the Baltic Sea, the Kattegat–Skagerrak Seas and off the west coast of Norway

Incidental mortality of harbour porpoises, Phocoena phocoena, from captures in fishing gear has been documented consistently as severe in some European waters. Since fishing effort varies greatly among regions, management units must be defined for more effective conservation of this species. In this study, analysis of mitochondrial DNA (mtDNA) restriction fragments was performed to investigate the population structure of harbour porpoises in the Baltic Sea, the joint Kattegat–Skagerrak Seas and off the west coast of Norway. Mitochondrial DNA of 65 harbour porpoises collected from three regions was analysed with nine restriction enzymes. Analysis of the heterogeneity in the frequency distribution of haplotypes among provisional subpopulations revealed significant differences, which supports the recognition of three different subpopulations and thus three separate management units. Furthermore, indices of haplotypic diversity (range: 0.211 to 0.628) and nucleotide diversity (range: 0.070 to 0.168) of these provisional subpopulations were much lower than for western North Atlantic subpopulations, which is consistent with the view that harbour porpoises in European waters, particularly in the Baltic Sea, are depleted. Received: 21 August 1996 / Accepted: 19 September 1996     

Monitoring the movements of harbour porpoises (Phocoena phocoena) with satellite telemetry

The movements of nine harbour porpoises, Phocoena phocoena (L.), in the Bay of Fundy and Gulf of Maine were tracked using satellite telemetry. Transmitters were attached to the porpoises in August 1994 and 1995 after they were captured near Grand Manan Island at the mouth of the Bay of Fundy. Tracking periods ranged from 2 to 212 d (mean 50 ± 65 d). Porpoises exhibited a high degree of individual variation in movement patterns; five moved out of the Bay of Fundy into the Gulf of Maine. The porpoise with the longest tracking period moved extensively throughout the Gulf of Maine. These data suggest that seasonal movement patterns of individual harbour porpoises are discrete and are not temporally coordinated migrations. Porpoises that moved out of the Bay of Fundy into the Gulf of Maine did so following the 92 m isobath, which may represent an important movement corridor. The movement of porpoises from the Bay of Fundy into the Gulf of Maine supports the hypothesis that harbour porpoises from these two regions comprise a single population at risk of entanglement in both Canadian and US fisheries. Received: 4 February 1997 / Accepted: 25 August 1997     

Mitochondrial DNA phylogeography of the harbour porpoise Phocoena phocoena in the North Pacific

Genetic structure and phylogeography of the harbour porpoise Phocoena phocoena in the North Pacific were examined using 358 bps sequences from the 5′ end of the mitochondrial DNA control region including those reported previously and newly obtained from the west Pacific. AMOVA and pairwise population φ _st estimates clearly revealed genetic differentiation between an east/south and a north/northwest group with the break along the Pacific Rim at British Columbia. In addition, nested clade phylogeographical analysis, neutrality tests, mismatch distribution analysis, genetic diversities and Mantel test, suggested that the observed genetic structure might have been influenced by contiguous range expansion with restricted gene flow in the direction from south to north along the North American coasts and east to west along the Pacific Rim in the middle to late Pleistocene.     

The population structure of the harbour porpoise,Phocoena phocoena,in Danish waters and part of the North Atlantic

A study of the homogeneity between putative stocks of Phocoena phocoena in the North Sea and inner Danish waters was performed using isozyme electrophoresis. Two polymorphic systems, mannose phosphate isomerase (MPI) and phosphoglucomutase (PGM) were used in the analysis. A two-locus homogeneity test showed an effect of season and locality on the genotypic distribution. This led to a division of the total sample into season and into the two localities, the inner Danish waters (IDW) and the North Sea. The samples were then compared to the Hardy-Weinberg expectations where a deficit in heterozygotes was observed in the North Sea sample in both systems and at the Pgm locus in the total sample, indicating a mixing of sub-populations. A hierarchical contingency table analysis, also based on the genotypic distribution, showed a combined effect of season and locality and only an insignificant effect of sampling period, thus supporting the division into season and locatily. The seasonal effect is further supported by earlier observations of a seasonal migration of harbour porpoises out of the Baltic in winter. A significant difference was observed between the two supposed sub-populations, IDW-summer and North Sea-summer samples, based on the genotypic distribution. This could also be a reflection of the sample sizes. On the basis of samples obtained from Canada, West Greenland and Holland a preliminary study of the population structure on a larger scale, comprising the North East and North West Atlantic, was performed. The results so far accord well with the hitherto accepted sub-populations of P. phocoena in the North Atlantic.     

Correlation between the seasonal distribution of harbour porpoises and their prey in the Sound,Baltic Sea

Low densities of harbour porpoises in winter (November–March) and high densities in summer (April–October) were found in the Sound, connecting the Baltic Sea and Kattegat. Due to their high energy requirements, it is hypothesized that the density of harbour porpoises is related to local prey abundance. This was tested by examining the stomach content of 53 harbour porpoises collected between 1987 and 2010 in the Sound (high season, 34 porpoises; low season, 19 porpoises). A total of 1,442 individual fish specimens from thirteen species were identified. Twelve of these were present in the high–porpoise density season and seven in the low-density season. The distribution of occurrence and the distribution of number of fish species were different between seasons, indicating a shift in prey intake between seasons. Furthermore, during the high-density season, the mean and total prey weight per stomach as well as the prey species diversity was higher. However, no difference was found in the number of prey species between the two seasons, indicating a higher quality of prey in the high-density season. Atlantic cod was found to be the main prey species in terms of weight in the high-density season while Atlantic herring and Atlantic cod were equally important during the low-density season. Prey availability and predictability are suggested as the main drivers for harbour porpoise distribution, and this could be caused by the formation of frontal zones in spring in the northern part of the Sound, leading to prey concentrations in predictable areas.     

Seasonal changes in inorganic nutrient concentration in the alexandria western harbour (Egypt)

Surface and bottom water samples were collected on a monthly basis from six locations in the Alexandria Western Harbour between April 2002 and March 2003. Total nitrogen, ammonia, nitrite, nitrate, total phosphorus, reactive phosphate and silicate were analysed. The average content of total nitrogen ranged from 81.1 to 65.7?µmol?l^?1 in the surface and bottom waters, respectively, while ammonia ranged from 13.77 to 15.79?µmol?l^?1 in surface and bottom waters, respectively. Also, the average concentration of nitrite was relatively higher in surface waters than in bottom waters (0.89 and 0.61?µmol?l^?1, respectively). The results of this study also indicated a considerable temporal variation in nitrate concentrations which ranged from 1.12 to 13.83?µmol?l^?1. Total phosphorus displayed an irregular pattern throughout the year, ranging from 1.9 to 11.8?µmol?l^?1 in surface waters and from 1.7 to 9.1?µmol?l^?1 in bottom waters. The results of PO₄-P analysis showed higher values in surface waters (0.28–2.75?µmol?l^?1) than in bottom waters (0.10–1.70?µmol?l^?1). The average concentration of silicates was relatively lower in the surface than in the bottom waters (8.97 and 10.1?µmol?l^?1, respectively). The analysis of variance (ANOVA) among seasons and sites revealed significant differences for ammonia, total nitrogen and phosphate, while nitrate showed no significant differences among stations. Finally, silicate did not show any significant variance among sites and seasons (ANOVA, P?>?0.05).     

Spatial trends in abundance of long-finned pilot whales, white-beaked dolphins and harbour porpoises in West Greenland

Data from an aerial line transect survey conducted off West Greenland during August–September 2007 were used to estimate the abundance of long-finned pilot whales (Globicephala melas), white-beaked dolphins (Lagenorhynchus albirostris) and harbour porpoises (Phocoena phocoena). The abundance of each species was estimated using mark-recapture distance sampling techniques to correct for perception bias, and correction factors for time spent at the surface were applied. The fully corrected abundance estimates were 8,133 long-finned pilot whales, 11,984 white-beaked dolphins and 33,271 harbour porpoises. Based on density surface modelling methods, a count model with a generalised additive model formulation was used to relate abundance to spatial variables. Response curves indicated that the preferred habitats were deep offshore areas in Midwest Greenland for pilot whales, deep water over steep seabed slopes in South Greenland for white-beaked dolphins and relatively shallow inshore waters in Midwest–South Greenland for harbour porpoises. The abundance estimates and spatial trends for the three species are the first obtained from Greenland.     

Abundance, growth and life cycle of the mesopelagic amphipod Primno abyssalis (Hyperiidea: Phrosinidae) in the Oyashio region, western subarctic Pacific

Abundance and life-cycle features of the mesopelagic hyperiid amphipod Primno abyssalis (formerly P. macropa) in the Oyashio region, western subarctic Pacific, were investigated using samples collected between July 1996 and July 1998. P. abyssalis was collected throughout the entire survey period, with abundance peaks occurring in spring to autumn. While all maturity stages of males and females were observed throughout the study period, the peak reproduction season was in summer. Instar analysis based on the segment number of the pleopod rami indicated that hatched juveniles molted 10 times before becoming adult males and 13 times before becoming adult females. Judging from the dry and ash-free dry weights of each instar, males and females continued to feed throughout the final instar stage. Based on cohort analysis of seasonal samples and laboratory observations on molting frequencies, growth in body length of P. abyssalis was linear with time, and estimated generation lengths were 2.3-3.8 years for females and 1.4-1.9 years for males. Brood size of females ranged from 66 to 337 and increased with increasing female body length. Lifetime fecundity, calculated as the sum of six successive broods, was 1,004. Compared with P. abyssalis in the southern Sea of Japan, those in the Oyashio region have a larger number of adult instars (six versus five for females, three 3 vs one for males), a lower growth rate (0.014 mm day^-1 vs 0.021 mm day^-1), and mature earlier (instar 13 vs instar 15 for females; instar 10 vs instar 11 for males). These characteristics are considered to be advantageous life-history traits to counteract higher niche competition within the mesopelagic community and higher predation pressure by mesopelagic fishes in the Oyashio region than in the Sea of Japan.     

Selective grazing of the isopod Idotea baltica between Fucus evanescens and F. vesiculosus from Kiel Fjord (western Baltic)

Grazing rates of the isopod Idotea baltica on Fucus evanescens and F. vesiculosus (Phaeophyta) were quantified in laboratory feeding preference experiments. Fucus species were offered alone (no-choice) or simultaneously (choice). In three of four no-choice experiments and in all four choice experiments, I. baltica significantly preferred F. vesiculosus to F. evanescens. F. evanescens recently immigrated into Kiel Fjord and has increased in abundance since 1990. One possible reason for the competitive success of this species may be that, compared to F. vesiculosus, it is less preferred by I. baltica, the most abundant mesograzer at the study site.     

Egg buoyancy of Baltic cod (Gadus morhua) and its implications for cod stock fluctuations in the Baltic

Successful spawning of Baltic cod (Gadus morhua L.) is restricted to the deep basins of the Baltic Sea and is dependent on abiotic conditions such as salinity and water oxygen content. Due to irregular inflows of saline water from the North Sea, the conditions for spawning fluctuate and consequently so does the cod stock. In May and June 1990 eggs were obtained from spawning cod caught off northern Gotland, Sweden. Our investigation revealed neutral egg buoyancy for Baltic cod at a salinity of 14.4±1.1 ppt, with a slight decrease some days before hatching. Today salinities of this magnitude occur only in the Bornholm basin, whereas in the Gdansk and Gotland basins the eggs sink toward the bottom and are exposed to lethal oxygen conditions.     

In-situ observations of Baltic herring (Clupea harengus membras) spawning behaviour in the Askö-Landsort area,northern Baltic proper

In a Baltic herring (Clupea harengus membras L.) spawning ground study, carried out in summer 1982 in the northern Baltic proper, spawning herring were encountered on two line transects on June 14. The spawning behaviour of minor groups as well as of a large school was studied in situ by four divers for approximately three hours. No behavioural differences or systematic coordinated behaviour between the sexes could be detected. Most of the spawning took place in a limited depth interval, 0.5 to 4 m, and Ceramium tenuicorne was the substrate most used.     

Abundance and seasonal variations of phytoplankton in the creek waters of western mangrove of Kachchh-Gujarat

The phytoplankton was assessed quantitatively and qualitatively in regard to their abundance in creek waters at three sites along the western mangrove of Kachchh. In total one hundred and four species of phytoplankton were identified. Among them 82 species diatoms (Bacillariophyceae), 16 species dinoflagellates (Dinophyceae), 3 species blue greens (Cyanophyceae) and 2 species were green algae. The density in all the three sites varied from 94,166.67 to 2,44,500 cells l(-1). The salinity ranged from 36 to 44 per thousand, temperature 17 to 35 degrees C and pH ranged from 7 to 8.9 respectively. These semi arid zone mangrove creek area having high densities were recorded during monsoon and early winter season.     

Diel vertical migration and feeding patterns of Mysis mixta (Crustacea,Mysidacea) in the Baltic Sea

The extent of the nocturnal vertical migration of Mysis mixta Lilljeborg varied between early July and late October (of 1985 and 1986) in a coastal area of the Baltic Sea. Migration was more restricted in early July and late October. Seasonal changes in surface light levels and transparency were sufficient to explain the observed differences. Mysids avoided light levels above 10^-4 lux throughout the study period. Smaller juveniles migrated higher up than larger juveniles and adults. A two-layered distribution with part of the population close to the bottom was observed at night. Zooplankton were more abundant in water layers above the main concentration of mysids. M. mixta fed on phytoplankton, detritus, copepods, cladocerans, rotifers and tintinnids. Diel changes in gut fluorescence indicated a higher intake of phytoplankton at night, but levels were low compared to primarily herbivorous zooplankton. Comparisons of stomach contents of mysids caught at the bottom in the evening and in the water column at night showed a higher ingestion of zooplankton at night and of detritus during the day. Mysids caught at the bottom at night had an intermediate diet. Copepods and cladocerans constituted between 90 and 100% of ingested material by weight in all mysid groups.     

Diets of four deep-water scaphopod species (Mollusca) in the North Atlantic and the Nordic Seas

The buccal pouch contents of four deep-water scaphopod (Mollusca) species, Pulsellum affine, Pulsellum teres, Siphonodentalium lobatum and Polyschides olivi, collected in the North Atlantic and the Nordic Seas, were examined. The buccal pouches of the examined scaphopod species contained almost exclusively foraminifers, which agrees with previous studies on shallow and deep-water scaphopods. The scaphopods seemed to be engulfing at least some of the most common foraminifer species, which are distributed in the cold waters of the Nordic Seas or the temperate waters in the northernmost part of the North Atlantic. About half of the food species (30 foraminifer species) occurred in only one scaphopod species, nearly always in very low numbers, and seemed to be an unimportant food source. The remaining and more frequent food species occurred in two or more scaphopod species. A similarity tree was calculated with parsimony and presence–absence coding of the food species in the scaphopods. This resulted in the similarity tree: 100%{P. teres 79%[P. affine 70%(P. olivi and P. lobatum)]}, when branch support was measured with percentage jackknife stability. A general trend was found towards larger food items being consumed by larger scaphopod species, indicated by the positive correlation between the size of the scaphopods and the food species. It is suggested that microdistribution of the foraminifers and the large individual size of the foraminifers may be important factors in avoiding predation by scaphopods.     

Distributional patterns of the eulitoral fauna near the isle of Hiddensee (Baltic Sea,Rugia)

In the eulitoral zone near the isle of Hiddensee (Baltic Sea) aggregated distribution is typical for the macrofauna. Only mussels are randomly distributed; they occur in low individual abundance. In contrast, Clark and Milne (1955) found random distribution to be the general rule for animals of the sublitoral zone.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.     

Red-list status and extinction risk of the world's whales,dolphins, and porpoises

To understand the scope and scale of the loss of biodiversity, tools are required that can be applied in a standardized manner to all species globally, spanning realms from land to the open ocean. We used data from the International Union for the Conservation of Nature Red List to provide a synthesis of the conservation status and extinction risk of cetaceans. One in 4 cetacean species (26% of 92 species) was threatened with extinction (i.e., critically endangered, endangered, or vulnerable) and 11% were near threatened. Ten percent of cetacean species were data deficient, and we predicted that 2–3 of these species may also be threatened. The proportion of threatened cetaceans has increased: 15% in 1991, 19% in 2008, and 26% in 2021. The assessed conservation status of 20% of species has worsened from 2008 to 2021, and only 3 moved into categories of lesser threat. Cetacean species with small geographic ranges were more likely to be listed as threatened than those with large ranges, and those that occur in freshwater (100% of species) and coastal (60% of species) habitats were under the greatest threat. Analysis of odontocete species distributions revealed a global hotspot of threatened small cetaceans in Southeast Asia, in an area encompassing the Coral Triangle and extending through nearshore waters of the Bay of Bengal, northern Australia, and Papua New Guinea and into the coastal waters of China. Improved management of fisheries to limit overfishing and reduce bycatch is urgently needed to avoid extinctions or further declines, especially in coastal areas of Asia, Africa, and South America.     

Managing a protected marine area for the conservation of critically endangered vaquita (Phocoena sinus Norris, 1958) in the Upper Gulf of California

We analysed fisheries trends in the northern region of the Gulf of California, within the Biosphere Reserve of the Upper Gulf of California and Colorado Delta River and the Vaquita Refuge Area, and suggest measures to protect the vaquita, Phocoena sinus. We compiled and analysed catch reports of artisanal fishermen in the three fishing communities of the Upper Gulf of California (San Felipe in the State of Baja California, and Golfo de Santa Clara and Puerto Peñasco in the State of Sonora) from 1995 to 2007. This information was categorised with respect to geographic information systems, and all fishing sites within two marine protected areas in the region were identified. In addition, from a survey based on direct interviews with artisanal fishermen in each of the three ports, we identified that 23% of fishermen will continue fishing despite on-going fishing buy-out programmes in the region. We suggest several specific courses of action to decrease the fishing impact on this critically endangered cetacean. However, given the critical situation of this critically endangered species, it is very uncertain whether enforcing a no-take zone within the biosphere reserve and the Vaquita Refuge Area, or even a wider fishing moratorium, will be enough to save this endangered species from extinction.     

Submarine experiments on benthic colonization of sediments in the western Baltic Sea. II. Meiofauna

From July, 1972 to February, 1973, meiofauna samples were taken from submerged platforms. Substrates were gravel, fine sand, and clayey mud. The individual samples consisted of 20 cm² 100 cm³. A diver collected the samples by hand. Some days after submersion of the platforms, colonization by meiofauna began. The submerged substrates were colonized almost exclusively by nematodes and harpacticoids; gastrotrichs were never present. In general, the harpacticoid fauna can be classified into two groups: the first, confined to the mesopsammon, did not colonize the platforms; the second, not limited to the interstitial habitat, did colonize. Two harpacticoid species, Ameira parvula and Danielssenia typica, were markedly dominant. The main migration route to the submerged platform was up the securing lines.Contribution no. 35 from the Sonderforschungsbereich 95, Kiel.