Potential Spatial Overlap of Heritage Sites and Protected Areas in a Boreal Region of Northern Canada

Abstract:  Under article 8-J of the Convention on Biological Diversity, governments must engage indigenous and local communities in the designation and management of protected areas. A better understanding of the relationship between community heritage sites and sites identified to protect conventional conservation features could inform conservation-planning exercises on indigenous lands. We examined the potential overlap between Gwich'in First Nations' (Northwest Territories, Canada) heritage sites and areas independently identified for the protection of conventional conservation targets. We designed nine hypothetical protected-area networks with different targets for woodland caribou ( Rangifer tarandus caribou ) habitat, high-quality wetland areas, representative vegetation types, water bodies, environmentally significant area, territorial parks, and network aggregation. We compared the spatial overlap of heritage sites to these nine protected-area networks. The degree of spatial overlap (Jaccard similarity) between heritage sites and the protected-area networks with moderate or high aggregation was significantly higher ( p < 0.001) than random spatial overlap, whereas the overlap between heritage sites and the protected-area networks with no aggregation was not significant or significantly lower ( p < 0.001) than random spatial overlap. Our results suggest that protected-area networks designed to capture conventional conservation features may protect key heritage sites but only if the underlying characteristics of these sites are considered. The Gwich'in heritage sites are highly aggregated and only protected-area networks that had moderate and high aggregation had significant overlap with the heritage sites. We suggest that conventional conservation plans incorporate heritage sites into their design criteria to complement conventional conservation targets and effectively protect indigenous heritage sites .     

Reproduction and life-cycle of the beachflea (<Emphasis Type="Italic">Orchestia gammarellus</Emphasis> (Pallas) (Crustacea: Amphipoda) at thermal and non-thermal sites in the intertidal of Iceland: how important is temperature?

The littoral fringe beachflea Orchestia gammarellus (Pallas) is a seasonal breeder over much of its range. Previous studies indicated that temperature was the most important factor initiating breeding while photoperiod appeared inconsequential. We tested the effect of temperature by comparing two populations at non-thermal sites with two populations at thermal sites in Iceland. At the non-thermal sites the species is probably close to its lower temperature tolerance limits, while potentially able to choose optimal temperatures at all times of the year at the thermal sites. The species was a seasonal breeder at all sites, but the breeding season started 2–3 months earlier at thermal sites. Breeding ended at about the same time at all sites. We conclude that photoperiod probably governs breeding season under constant thermal conditions, and this is also supported by observations on laboratory stocks. At the thermal sites the animals became sexually mature in a year or less, as is the case where the species has been studied at lower latitudes, while at the non-thermal sites Icelandic animals, apparently uniquely, need 2 years to become sexually mature.     

The mating system and alternative reproductive behaviors ofDendrobias mandibularis (Coleoptera: Cerambycidae)

Summary Adults ofDendrobias mandibularis fed at sites where sap oozes from the stems of desert broom,Baccharis sarothroides. These sites were used by only one individual at a time. Males practiced alternative reproductive tactics, and were separated into two distinct morphs. Major males had enlarged mandibles, were found significantly more frequently at feeding sites than elsewhere on the food plants, and defended the feeding sites to gain access to females that visited the sites to feed. Minor males had small mandibles, were found significantly more frequently in foliage of the food plant than at feeding sites, and usually did not defend feeding sites. Mandibles were used in aggressive interactions, which were always won by larger males. Mating occurred at feeding sites, on stems, and in foliage of the food plant. Major males were observed mating nearly twice as often as minor males. Major males mated significantly more frequently at feeding sites than in foliage; the reverse was true of minor males. Minors occasionally occupied and mated at feeding sites. They were unable to defend feeding sites against majors, but did so occasionally against other minors. Differences in frequency, mating success, and behavior of the morphs appeared to be linked to differences in environmental conditions between the two years of this study. This study demonstrated the importance of spatial distribution of food resources in the evolution of the mating system ofDendrobias mandibularis.     

CUSUM environmental monitoring in time and space

We consider the situation where there are n sampling sites in an area, with an environmental variable measured at some or all of the sites at m sample times. We assume that there is interest in knowing whether the environmental variable displays systematic changes over time at the sites. A cumulative sum type of analysis with associated randomization tests has been proposed before for this situation, when there is negligible correlation between the observations in different times at one site, and no correlation between the results at different sites. A modification that allows for serial correlation at the individual sites but with no correlation between sites has also been proposed before. In the present paper we discuss how the method can be modified further to allow for spatial correlation between the sites, by applying it only to a reduced set of sites that are far enough apart to give effectively independent results. Simulation results indicate that this strategy is effective providing that the level of spatial correlation is not too high.     

Use of data on avian demographics and site persistence during overwintering to assess quality of restored riparian habitat

Monitoring responses by birds to restoration of riparian vegetation is relatively cost-effective, but in most assessments species-specific abundances, not demography, are monitored. Data on birds collected during the nonbreeding season are particularly lacking. We captured birds in mist nets and resighted banded birds to estimate species richness and diversity, abundance, demographic indexes, and site-level persistence of permanent-resident and overwintering migrants in remnant and restored riparian sites in California. Species richness in riparian remnants was significantly higher than in restored sites because abundances of uncommon permanent residents were greater in remnants. Species richness of overwintering migrants did not differ between remnants and restored sites. Responses among overwintering migrants (but not permanent residents) to remnant and restored riparian sites differed. Capture rates were higher in remnant or restored riparian sites for 7 of 10 overwintering migratory species. For Lincoln's Sparrows (Melospiza lincolnii) and White-crowned Sparrows (Zonotrichia leucophrys) proportions of older birds were significantly higher in remnants, even though capture rates of these species were higher in restored sites. Overwinter persistence of 4 migrant species was significantly higher in remnant than in restored sites. A higher proportion of Hermit Thrushes (Catharus guttatus, 56.3%), older Fox Sparrows (Passerella iliaca, 57.1%), Lincoln's Sparrows (59.7%), and White-crowned Sparrows (67.8%) persisted in remnants than restored sites. Our results suggest restored riparian sites provide habitat for a wide variety of species in comparable abundances and diversity as occurs in remnant riparian sites. Our demographic and persistence data showed that remnants supported some species and age classes to a greater extent than restored sites.     

Prioritizing urban marine habitats for conservation

Urban coastal wetlands and adjoining coves and embayments can provide habitat for significant numbers of waterbirds, despite being subject to high levels of stressors from human activities. Yet to date little emphasis has been placed on identifying these areas and prioritizing them for conservation. In this study I outline a three-step process to identify and prioritize local sites for conservation using waterbird abundance and diversity and an index of the risk to a site from marine development, and apply it to a series of urban coastal sites in two North Atlantic estuaries located in the northeast US. By combining waterbird abundance and species richness with the risk from marine development I generated a ranked list of sites with the highest listed sites having high bird diversity and low risk from development. From this list individual sites can be prioritized for conservation, and various protection scenarios can be evaluated and compared. For example, 7 of the top 10 ranked sites in Boston Harbor, combined with sites already protected under local, state, or federal statutes, represented over half of the total bird diversity in the Harbor. Similarly, in Narragansett Bay 6 of the top 10 sites when combined with sites already protected represent 48.8% of the Bay’s bird diversity. Formally protecting these sites, all of which are at relatively low risk from marine development, could result in the conservation of considerable waterbird habitat at low economic cost (i.e., from loss of development potential). Other ranking scenarios (by bird diversity alone, or by risk from marine development) were also evaluated and compared to the combined ranking. Identification of sites with high bird diversity and low risk from development could provide important information for local land acquisition groups and planning boards when considering options for the conservation of urban coastal habitats.     

Genetically isolated stocks of orange roughy (Hoplostethus atlanticus), but not of hoki (Macruronus novaezelandiae), in the Tasman Sea and Southwest Pacific Ocean around New Zealand

Restriction fragment-length polymorphisms of mitochondrial (mt) DNA, generated by six-base restriction enzymes, were used to examine the stock structure of the two major commercial species in New Zealand fisheries, orange roughy (Hoplostethus atlanticus Collett) and hoki (Macruronus novaezelandiae Hector). Samples of orange roughy from six spawning sites around New Zealand and one site off Tasmania show significant genetic heterogeneity. Samples from two sites around the south of New Zealand were genetically similar to each other, but dissimilar to samples from all other sites. The common haplotype observed in northern sites was absent from the two southern sites. Low numbers of unique haplotypes were restricted to the Challenger Plateau in the Tasman Sea. There was no significant genetic heterogeneity in five samples of hoki from two spawning sites off New Zealand and one site off Tasmania.     

Nest site limitation and facultative polygyny in the ant Leptothorax longispinosus

Summary The ant L. longispinosus displays geographic variation in its pattern of facultative polygyny (Fig. 2). In nature, nest density and frequency of multiple queening are positively associated over three sites. A putative causal relation between availability of vacant nest sites and polygyny was examined in New York, where a plot was seeded with additional nest sites and monitored for 24 months. Both queen number and worker number per nest on the experimental plot were reduced relative to controls (Fig. 4, Fig. 5), indicating that scarcity of available nest sites influences the pattern of polygyny in this species. The observed demographic changes resulted from fractionation of existing colonies; adding nest sites induced polydomy. Although numbers of adult ants changed with addition of nest sites, the numbers of immatures were no different after 2 years (Table 1), suggesting that the population was undergoing growth to expand into the additional sites. These results are the first direct experimental evidence linking polygyny to an ecological parameter for any ant species.     

Choice and utilization of oviposition sites by female Calopteryx maculata (Odonata: Calopterygidae)

Summary Females of the damselfly Calopteryx maculata (de Beauvois) initially choose the larger of a pair of adjacent oviposition sites, about 70% of the time (Table 1), or whichever of two equal sized sites had other ovipositing females on it (about 88% of the time-Table 2). These criteria for initial choice between a pair of sites also interact. Incoming females generally (57 to 74% of the time-Table 3) joined others on the small site rather than ovipositing alone at the adjacent, bigger site. When pairs of large and small sites were replicated across eight locations, there were nonsignificant trends towards greater utilization (eggs laid) of the larger of a pair of oviposition sites within locations (Table 4). The lack of agreement between initial choice and utilization shows that other factors besides size are important in the choice and use of oviposition sites. These include disturbance by males, the presence of other females and choice criteria that can only be assessed during oviposition. When all sites at the eight locations were equal in size, there was considerable day to day and location to location variation in eggs laid (Fig. 1). Viewed over periods of several days, some sites are obviously less attractive than others in terms of cumulative numbers of eggs laid at them. When the amount of vegetation was varied among locations, those with the bigger oviposition sites were used more often, somtimes significantly so, but there were also significant reversals (small sites used more often) (Table 5, Fig. 1). Thus, there is no simple effect of size on the utilization of oviposition sites by Calopteryx maculata females, despite a clear tendency for females to make initial choices based on this criterion. The considerable among and within location variation in number of eggs laid may reflect additional choice criteria or the interaction of size, the presence of other females, disturbance, and location.     

Experimental tests of the information-center hypothesis with black vultures (Coragypsatratus) and turkey vultures (Cathartesaura)

In field tests of the information-center hypothesis (ICH) in south Texas with black vultures (Coragyps atratus) and turkey vultures (Cathartes aura), large carcasses were provided and kept under continuous observation. The use vultures made of these bait sites and their patterns of arrival were recorded to evaluate predictions derived from the ICH. Turkey vultures discovered most bait sites (30 of 31) first, but frequently were displaced from the food by later-arriving black vultures. This competitive exclusion by black vultures limited subsequent feeding opportunities for turkey vultures sufficiently that few (27%) returned on subsequent days to bait sites they had previously visited. I found no evidence that those turkey vultures that did return to bait sites acted as leaders for groups of naive birds and led them to bait sites – knowledgeable and naive turkey vultures did not arrive at bait sites together, and groups arriving at bait sites were not larger on subsequent days than on the first days carcasses were available. In contrast, a significantly larger percentage (47%) of knowledgeable black vultures returned to bait sites they had visited on previous days, and the first groups of black vultures arriving at bait sites on subsequent days were significantly larger than the equivalent groups on first days. Nine flocks of black vultures that arrived on subsequent days at bait sites before sunrise (which suggests the birds had commuted directly from a roost) contained knowledgeable birds, and two of these flocks contained both knowledgeable and naive individuals. Overall, 10 of 54 naive tagged black vultures (18.5%) arrived at bait sites under circumstances that suggested they had followed conspecifics to the food from a roost. However, most black vultures apparently found carcasses through independent search or by using local enhancement. Therefore, I conclude that while following from roosts to food sites is a strategy used by black vultures, at this study site it is one they use relatively infrequently. Received: 20 February 1997 / Accepted after revision: 28 June 1997     

西方国家工业污染场地管理经验及其对中国的借鉴

近年来,随着＂退二进三＂、＂退城进园＂和＂产业转移＂等政策的实施,中国几乎所有的大中城市正面临着重污染工业企业关闭和搬迁问题,城市出现大量工业遗留和遗弃场地。这些受污染的工业场地多存在较为严重的土壤、地表水和地下水污染;另外,工业污染场地的延迟再开发,会产生生活环境变差、就业机会减少、甚至社会不稳定因素增加等社会影响。所以,城市工业污染场地严重威胁着城市人居环境安全和公众健康,阻碍着城市建设和经济发展。面对工业污染场地目前存在的问题,国家及部分地方政府已针对污染场地的管理、修复及其再开发颁布了诸多文件和技术规范标准。然而,由于工业场地类型的多样性和环境管理学科的交叉性,中国城市工业污染场地的环境管理工作仍处于起步阶段,亟需完善。美国、英国和加拿大经过20~30年的发展已经在工业污染场地管理方面积累了丰富的经验,他们不仅在环境管理中体现了人体健康风险评估的理念,而且还立足本国实际出台了相关的法律法规,明确了污染场地的责任主体,实现了＂污染者付费＂的原则,同时还建立了各自的污染场地治理优先名录,实现了污染场地管理的信息化和网络化。本文鉴于对这些经验的比较分析,结合我国实际,就城市工业污染场地的环境管理提出了现阶段亟须解决的两大问题。首先,制定工业污染场地管理的专门法律,明确污染场地的责任主体。我国现有的与污染场地有关的国家法律法规,都比较笼统地提出了污染场地的利益相关方,缺乏具有可操作性的细则和威慑力的责任追究条款。对于我国这样地域辽阔、自然地理条件差异大、经济水平不均衡的国家来说,通过地方法律法规的建立明确污染场地的责任主体是一个重要的尝试。其次,构建污染场地健康风险评估系统。我国城市工业污染场地涉及诸多工业行业、污染类型繁多复杂。因此,在全国范围内对城市工业污染场地进行排查、建立优先污染场地名录是构建污染场地风险评估系统的重要内容。此外,我国现有的土壤质量标准和场地评估规范仍存在诸多缺陷,无法满足当前国家城市工业污染场地的管理需要。所以,完善场地评估的技术规范和相关标准将为污染场地风险评估系统的构建提供基础性保障。本文的论述和观点可为我国工业企业关停或搬迁遗留地的决策管理和污染场地管理体系的建立提供有意义的参考和借鉴。     

Effectiveness of multiple release sites in reintroduction of Persian fallow deer

Releasing animals in more than one location may increase or decrease the probability of success of a reintroduction project, yet the question of how many release sites to use has received little attention. We used empirical data from the reintroduction program of the Persian fallow deer (Dama mesopotamica) (Galilee region in northern Israel) in an individual-based spatially explicit simulation model to assess the effects of releasing deer from multiple sites. We examined whether multiple release sites increase reintroduction success, and if so, whether the optimal number of sites for a given scenario can be determined and whether the outcome differs if animals are released alternately (i.e., the location of the release alternates yearly between sites) or consecutively (i.e., one release site is used for several years, then another is used, and so forth). We selected 8 potential release sites in addition to the original site and simulated the release of 180 individuals at a rate of 10 individuals per year in different combinations of the original site and 1-4 additional sites. In our model, releasing animals into the wild at multiple sites produced higher population growth and greater spatial expansion than releasing animals at only one site and a consecutive-release approach was superior to an alternate-release approach. We suggest that through the use of simulation modeling that is based on empirical data from previous releases, managers can make better-informed decisions regarding the use of multiple release sites and greatly improve the probability of reintroduction success.     

An integrated approach for predicting fates of reintroductions with demographic data from multiple populations

We devised a novel approach to model reintroduced populations whereby demographic data collected from multiple sites are integrated into a Bayesian hierarchical model. Integrating data from multiple reintroductions allows more precise population-growth projections to be made, especially for populations for which data are sparse, and allows projections that account for random site-to-site variation to be made before new reintroductions are attempted. We used data from reintroductions of the North Island Robin (Petroica longipes), an endemic New Zealand passerine, to 10 sites where non-native mammalian predators are controlled. A comparison of candidate models that we based on deviance information criterion showed that rat-tracking rate (an index of rat density) was a useful predictor of robin fecundity and adult female survival, that landscape connectivity and a binary measure of whether sites were on a peninsula were useful predictors of apparent juvenile survival (probably due to differential dispersal away from reintroduction sites), and that there was unexplained random variation among sites in all demographic rates. We used the two best supported models to estimate the finite rate of increase (λ) for populations at each of the 10 sites, and for a proposed reintroduction site, under different levels of rat control. Only three of the reintroduction sites had λ distributions completely >1 for either model. At two sites, λ was expected to be >1 if rat-tracking rates were <5%. At the other five reintroduction sites, λ was predicted to be close to 1, and it was unclear whether growth was expected. Predictions of λ for the proposed reintroduction site were less precise than for other sites because distributions incorporated the full range of site-to-site random variation in vital rates. Our methods can be applied to any species for which postrelease data on demographic rates are available and potentially can be extended to model multiple species simultaneously.     

Assessment of the impacts of municipal solid waste dumps on soils and plants

The study aimed at evaluating the impacts of open municipal solid wastes dumps on soil and vegetation near the main roads linking major cities in Nigeria. We hypothesised that the metals from the wastes exerted substantial impacts at the dump sites which affect the soil and plants. Data were analysed from five dump sites and five control sites. The result revealed that the effects of the heavy metals (HM) were significant and higher at the dump sites where their concentrations were far above the EU, and Canadian environmental quality permissible limits for agricultural soils and vegetation. In contrast with dump sites, a significant relationship (R²?=?0.70; p??Cr?>?Pb at both dump sites and control sites. Further study on the effects of more HM on soil and plant is recommended in the area. Recycling and bio-phytoremediation processes should also be introduced.     

Ecological impacts on the limpet Lottia gigantea populations: human pressure over a broad scale on island and mainland intertidal zones

Here long-term monitoring data taken at 33 sites in southern and central California coast and islands were used to evaluate the size structure of the large intertidal limpet, Lottia gigantea in restricted-access and in easily accessible intertidal zones that encompass a wide range of ecological variables. Using multi-dimensional analysis of population size structures, we found that sites on islands and strictly protected mainland sites have significantly larger median limpet sizes and a greater range of limpet sizes than unprotected mainland sites, while no pattern occurs in latitudinal or regional comparison of sites. Although intertidal predators such as oystercatchers were not the primary focus of the monitoring efforts, extensive natural history notes taken during sampling visits support the argument that predation was not a primary cause for the size structure differences. Finally, substratum differences were determined not to have biased the observation of larger limpets in protected sites. In regard to human interactions with limpets, we conclude that the degree of enforcement against poaching is the better predictor of limpet size structure than proximity to population centers or visitation to intertidal sites.     

Swimming performance trade-offs across a gradient in community composition in Trinidadian killifish (Rivulus hartii)

The impacts of predation and competition on life history, behavioral, and morphological traits are well established for many organisms, but effects on locomotor performance have received relatively little attention. We examined variation in sprint speed and critical swimming speed (U(crit), a measure of stamina) in the Trinidadian killifish (Rivulus hartii) across a gradient of ecological communities. R. hartii are located in (1) "high-predation" sites with large, piscine piscivores, (2) "Rivulus-guppy" sites with guppies, and (3) "Rivulus-only" sites with only R. hartii. R. hartii suffer higher mortality in high-predation sites. In Rivulus-guppy sites, population densities are reduced and growth rates increased compared with Rivulus-only sites, which likely represent indirect effects of guppy predation on young R. hartii. We show a significant negative relationship, suggesting a trade-off, between sprint speed and endurance; Rivulus from high-predation sites were faster sprinters but had reduced critical swimming speeds. This trade-off was also apparent in correlations of the nine population means. At the individual level, the correlation was weaker and only significantly negative when all nine populations (three from each site) were pooled and values were not corrected for body size. Sex had a significant effect on U(crit), with females having a lower U(crit), but sexes did not differ in sprint speed. Fish from high-predation sites also exhibited increased tail lengths and fineness ratios compared to sites without large predators. The two low-predation sites showed no statistical differences in locomotor performance or morphology.     

The effects of catchment land use on water quality and macroinvertebrate assemblages in Otara Creek,New Zealand

The effect of catchment land use on water quality and macroinvertebrate communities was examined by using data gathered during a 2004 reconnaissance of nine sites in the Otara Creek, New Zealand. Data collected included macroinvertebrate, water chemistry and sediments characteristics. Macroinvertebrate data were used in metric and index calculations. A total of 61 macroinvertebrate taxa, with 3032 total individuals, were identified from the macroinvertebrates samples collected from nine sites in Otara Creek. The greatest number of macroinvertebrate taxa was recorded within bush sites (mean>25), while the urban sites had the least number of taxa (mean=10). Pasture sites were intermediate with the mean>17. Taxa number differed significantly across land use. Mean macroinvertebrates abundance varied across the sites and land uses. The highest macroinvertebrates mean abundance was recorded in urban and pasture sites, while bush sites had significantly lower mean abundance. Physico-chemical parameters decreased from bush toward urban streams. Biotic indices were sensitive to changes in macroinvertebrates community structure across land uses with mean scores decreasing from bush to urban and pasture streams. Ordination of biological data showed a clear separation of bush from urban and pastures streams. Analysis of similarities revealed significant differences in macroinvertebrates between both stream groups and land-use groups. The observed macroinvertebrate assemblage pattern was best correlated with a single variable, conductivity, temperature, turbidity, nitrate and dissolved oxygen. The combination of these environmental variables best explained the changes in the macroinvertebrate assemblages between sites. This study demonstrates that catchment land use may significantly affect the water quality and macroinvertebrate communities in an ecosystem.     

甘肃兴隆山自然保护区濒危马麝(Moschus sifanicus)秋季利用生境特征

于2006~2007年9~10月间采用样线样带法研究了甘肃兴隆山自然保护区马麝的秋季生境利用特征,共布设286个空白对照样地和55个利用样地,测量并比较两类样地内的海拔等17个生境变量.结果表明,马麝秋季利用样地的乔木密度(0.90±0.14)和灌木均高(1.92 m±0.53 m)显著低于非利用样地(乔木密度1.35±0.07;灌木均高3.01 m±0.53 m),而且距水源距离(<1 000 m,76.37%)和人为干扰活动距离(<1 000 m,76.36%)较近的中下坡位生境(82.82%)(P<0.05).对喜好生境变量的主成分分析表明,地理因子(由海拔、水源距离、植被类型和坡向构成)是制约兴隆山马麝秋季栖息地选择的首要因子,此外,郁闭度因子(由郁闭度和坡度构成)、食物因子(由食物多度和乔木胸径构成)和隐蔽因子(由隐蔽度和避风性构成)也是影响兴隆山马麝秋季生境选择的重要因素.由于秋季对食物和水源的强烈选择,兴隆山马麝对生境隐蔽性和距人为干扰距离的选择强度较低,即承受较大强度的人为干扰.表5参31     

Protected area characteristics that help waterbirds respond to climate warming

Protected area networks help species respond to climate warming. However, the contribution of a site's environmental and conservation-relevant characteristics to these responses is not well understood. We investigated how composition of nonbreeding waterbird communities (97 species) in the European Union Natura 2000 (N2K) network (3018 sites) changed in response to increases in temperature over 25 years in 26 European countries. We measured community reshuffling based on abundance time series collected under the International Waterbird Census relative to N2K sites’ conservation targets, funding, designation period, and management plan status. Waterbird community composition in sites explicitly designated to protect them and with management plans changed more quickly in response to climate warming than in other N2K sites. Temporal community changes were not affected by the designation period despite greater exposure to temperature increase inside late-designated N2K sites. Sites funded under the LIFE program had lower climate-driven community changes than sites that did not received LIFE funding. Our findings imply that efficient conservation policy that helps waterbird communities respond to climate warming is associated with sites specifically managed for waterbirds.     

Seagrass and algal beds as nursery habitats for tiger prawns (Penaeus semisulcatus and P. esculentus) in a tropical Australian estuary

We evaluated the importance of seagrass and algae to two species of tiger prawns (Penaeus semisulcatus and P. esculentus) by detailed sampling at four sites (two seagrass, two algae) in the Embley River estuary, and through sampling 26 sites in 7 adjacent estuaries at one time of year. Samples of tiger prawns were collected in the Embley River estuary with a small beam trawl at night every 2 wk from September to May for 2 yr (1990 to 1992). The two seagrass sites, which were 11 and 13 km from the river mouth, showed less seasonal variation in salinity than the two algal sites, which were 15 and 20 km from the river mouth. The algal beds at the two upstream sites almost disappeared during the wet season, but the biomass of seagrass did not change significantly between the wet and dry seasons. The grooved tiger prawn (P. semisulcatus), the main species at all sites, comprised 88% of the total tiger prawn catch over the two years. They were found at all sites during the pre-wet season, but after the onset of the wet season, they disappeared along with the algae, from the upstream sites. The brown tiger prawn (P. esculentus) was found almost exclusively (97% of the total catch) on the seagrass sites downstream. In the study of several estuaries, juvenile P. semisulcatus were caught at all 26 sites, and P. esculentus were caught in much smaller numbers, at 16 sites. Approximately equal numbers of P. semisulcatus were caught in seagrass and algal beds in the pre-wet season. Very few individuals >10 mm carapace length of either species, were caught. The results from this study highlight the importance of algal beds during the pre-wet season as nursery areas for one species of tiger prawn (P. semisulcatus).