The Hudson-Raritan Estuary as a crossroads for distribution of blue (Callinectes sapidus), lady (Ovalipes ocellatus), and Atlantic rock (Cancer irroratus) crabs

Blue (Callinectes sapidus)(Portunidae),lady (Ovalipes ocellatus)(Portunidae), and Atlantic rock (Cancer irroratus) (Cancridae) crabs inhabit estuaries on the northeast United States coast for parts or all of their life cycles. Their distributions overlap or cross during certain seasons. During a 1991–1994 monthly otter trawl survey in the Hudson-Raritan Estuary between New York and New Jersey, blue and lady crabs were collected in warmer months and Atlantic rock crabs in colder months. Sex ratios, male:female, of mature crabs were 1:2.0 for blue crabs, 1:3.1 for lady crabs, and 21.4:1 for Atlantic rock crabs. Crabs, 1286 in total, were subsampled for dietary analysis, and the dominant prey taxa for all crabs, by volume of foregut contents, were mollusks and crustaceans. The proportion of amphipods and shrimp in diets decreased as crab size increased. Trophic niche breadth was widest for blue crabs, narrower for lady crabs, and narrowest for Atlantic rock crabs. Trophic overlap was lowest between lady crabs and Atlantic rock crabs, mainly because of frequent consumption of the dwarf surfclam (Mulinia lateralis) by the former and the blue mussel (Mytilus edulis) by the latter. The result of cluster analysis showed that size class and location of capture of predators in the estuary were more influential on diet than the species or sex of the predators.

Niche measures and feeding strategies of Barbodes gonionotus Bleeker and Oreochromis spp. from a ricefield in Bangladesh

Intra-and interspecific virtual niche measures and feeding strategies of Barbodes gonionotus and Oreochromis spp. were studied from a rice field in Bangladesh. Appropriateness and ease of interpretation of different indices were evaluated. Small sizes of both species had a relatively wider dietary breadth and used many of the resource categories available to them than the large size groups, though none were generalist feeder. The dietary overlap of large B. gonionotus on the small was greater than the reverse, but biologically insignificant. While the dietary overlap of large Oreochromis spp. on the small was significantly greater. Interspecific dietary width was relatively broader for B. gonionotus than Oreochromis spp. and overlap of B. gonionotus on Oreochromis spp. was significantly greater than the reverse. Evidence of significant intraspecific dietary overlap between the two sizes of tilapia reflects strong competition and cautions for mixed-size stocking in rice-fish system. Besides, there seem fewer opportunities for habitat segregation between B. gonionotus and Oreochromis spp., due to the significant interspecific dietary overlap of the former on the latter in rice-fish system. Tilapia specialized on periphytic detrital aggregate while silver barb tended to consume aquatic macrophytes and molluscs. Small sizes of B. gonionotus should be preferred for rice-fish integration over the Oreochromis spp. due to their broader niche width and pronounced ontogenetic dietary shifts with the aging of the stock.

Diet and feeding ecology of two sizes of Barbodes gonionotus (=Puntius gonionotus) and Oreochromis sp. in ricefields in Bangladesh

Fish culture experiments were conducted to compare and evaluate the feeding pattern and strategies, daily ration, gastric evacuation rates, dietary breadth, similarity and overlap of silver barb, Barbodes gonionotus, and tilapia, Oreochromis sp. (natural hybrid of O. mossambicus x O. niloticus) in a rice-fish system. B. gonionotus was found to be a macrophtophagous column feeder while Oreochromis sp. was a detrivorous benthophagic browser. Ontogenic shifts in diet were clearly observed in B. gonionotus while absent in Oreochromis sp. For both species, daily food ration for the small fish was twice as large as that for the large fish. Mean rates of gastric evacuation were 0.18 h super(1) for small and 0.05 h super(1) for large B. gonionotus and 0.09 h super(1) and 0.14h super(1) for small and large Oreochromis sp., respectively. In terms of intraspecific dietary width, the smaller sized individuals of both species had a wider dietary niche than the larger conspecifics. Larger fish increased their specialization and reliance on few food items with increasing size and competitive ability. When both species were reared together, B. gonionotus showed a wider niche width than tilapia. Wider interspecific niche width of B. gonionotus compared to that of tilapia and significant interspecific dietary overlap is likely to result in suppression of the growth of tilapia in mixed culture due to: 1) a high degree of specialization and reliance of tilapia on food of low-nutrient value, and 2) slower gastric evacuation rates as compared to B. gonionotus, which would allow B. gonionotus to outgrow similar sized tilapia.

Microhabitat breadth of fish community along the Vamanapuram River, south Kerala

The microhabitat breadth of Vamanapuram River fish community was studied in detail. The microhabitat variables selected were relative depth, focal point velocity, water column depth, mean water velocity and substrate. Puntius filamentosus had the highest breadth in three dimensions in both stream and river habitats showing a generalistic mode of resource utilization. Garra mullya, Labeo dero and Glossogobius giuris are specialists in the usage of microhabitat variables in the stream habitat while these are G. mullya, Etroplus maculatus and Aplocheilus lineatus in river habitat. Danio aequipinnatus showed extreme variations along focal point velocity variable in both habitats indicating an. opportunistic behaviour.

Height-depth (breadth) relationship of shells in the backwater oyster Crassostrea madrasensin (Preston) of the Cochin harbour

A study of the height-depth relation in the Indian backwater oyster Crassostrea madrasensis (Preston) was carried out. The plot of height against depth showed an exponential trend and a relationship of the form H = ADB. Plot of height against depth also showed larger deviations in height for oysters with greater depth. Analysis showed that variations in height do not result in corresponding variations in depth, particularly in oysters with increased height.

Enabling Sensor* Interoperability, Portland, Maine, October 16-18 2006: workshop proceedings

The ACT workshop "Enabling Sensor Interoperability" addressed the need for protocols at the hardware, firmware, and higher levels in order to attain instrument interoperability within and between ocean observing systems. For the purpose of the workshop, participants spoke in tern of "instruments" rather than "sensors," defining an instrument as a device that contains one or more sensors or actuators and can convert signals from analog to digital. An increase in the abundance, variety, and complexity of instruments and observing systems suggests that effective standards would greatly improve "plug-and-work" capabilities. However, there are few standards or standards bodies that currently address instrument interoperability and configuration. Instrument interoperability issues span the length and breadth of these systems, from the measurement to the end user, including middleware services. There are three major components of instrument interoperability including physical, communication, and application/control layers. Participants identified the essential issues, current obstacles, and enabling technologies and standards, then came up with a series of short and long term solutions. The top three recommended actions, deemed achievable within 6 months of the release of this report are: A list of recommendations for enabling instrument interoperability should be put together and distributed to instrument developers. A recommendation for funding sources to achieve instrument interoperability should be drafted. Funding should be provided (for example through NOPP or an IOOS request for proposals) to develop and demonstrate instrument interoperability technologies involving instrument manufacturers, observing system operators, and cyberinfrastructure groups. Program managers should be identified and made to understand that milestones for achieving instrument interoperability include a) selection of a methodology for uniquely identifying an instrument, b) development of a common protocol for automatic instrument discovery, c) agreement on uniform methods for measurements, d) enablement of end user controlled power cycling, and e) implementation of a registry component for IDS and attributes. The top three recommended actions, deemed achievable within S years of the release of this report are: An ocean observing interoperability standards body should be established that addresses standards for a) metadata, b) commands, c) protocols, d) processes, e) exclusivity, and f) naming authorities.[PDF contains 48 pages]

Neues aus der Selektionsforschung am Ostseedorsch

In account of the decision of the IBSFC (International Baltic Sea Fisheries Commission) to admit alternative codend constructions to the presently legal of diamond meshes with 120 mm mesh opening, since seven years a vivid research activity is encouraged at the fishing technology institutions around the Baltic. Though a center of gravity in this field of research lies in the EUproject BACOMA (participants Finland Sweden, Denmark) also the corresponding national institutes of other Baltic countries (Germany, Poland, Russia) have been active with similar investigations. German experiments in 1999 dealt with the effect of the use of netting made of double instead of single yarn on the selectivity. Further research was done on modifications of codends made from netting turned 90° from its original orientation and on simplified versions of the so-called Multipanel codend which consists of three equal diamond and three square mesh panels. The experiments demonstrated on the one hand a definite deterioration of the selective properties in a codend made from double instead of single yarn. Constructional changes in codends made from netting turned 90° on the other hand brought a further improvement of the selectivity of such codends. Finally, the investigations on the Multipanel codend revealed the overwhelming influence of the square mesh panels on the selectivity success. If in a conventional diamond codend three windows are cut out starting 50 cm from the real end of the codend in such a way that the remaining parts have the same breadth as the square mesh panels to insert, the selective effect of such a codend is remarkably improved. According to further preliminary tests this seems to be nearly independent from the type of material used.

Aspects of the biology of coarse fish in the Dorset Stour

Some of the results from an investigation of five species of coarse fish, in the Stour River, carried out from 1968-1978 are presented in this article. The species involved were: Rutilus rutilis, Leuciscus leuciscus, L. cephalus, Esox lucius and Perca fluviatilis : which are of particular interest to anglers. Although these species show some similarities, as in the shape of the annual and seasonal growth curves, in most other respects each species occupies a distinct niche in the ecosystem and has a life-history strategy peculiar to itself. In this study only 5 species were investigated. When all the species present are considered the relationships or diversities suggested here will therefore be made far more complex.

The Ribble. Portrait of an estuary

Blackpool, Lytham St. Anne's and Southport are household names as popular leisure and holiday resorts the length and breadth of the land. Their location at the mouth of the estuary of the River Ribble is much less well known, yet this same estuary is of paramount importance to both the economy and the environment of North West England. Indeed, the Ribble Estuary is of international importance for interests as diverse as wintering and migrating wild birds on one hand to the modern aerospace industry on the other. This brochure provides a brief introduction to the estuary of the River Ribble including a historic overview of the people living near the estuary, agriculture and wildlife.

Postrelease survival, vertical and horizontal movements, and thermal habitats of five species of pelagic sharks in the central Pacific Ocean

From 2001 to 2006, 71 pop-up satellite archival tags (PSATs) were deployed on five species of pelagic shark (blue shark [Prionace glauca]; shortfin mako [Isurus oxyrinchus]; silky shark [Carcharhinus falciformis]; oceanic whitetip shark [C. longimanus]; and bigeye thresher [Alopias superciliosus]) in the central Pacific Ocean to determine species-specific movement patterns and survival rates after release from longline fishing gear. Only a single postrelease mortality could be unequivocally documented: a male blue shark which succumbed seven days after release. Meta-analysis of published reports and the current study (n=78 reporting PSATs) indicated that the summary effect of postrelease mortality for blue sharks was 15% (95% CI, 8.5–25.1%) and suggested that catch-and-release in longline fisheries can be a viable management tool to protect parental biomass in shark populations. Pelagic sharks displayed species-specific depth and temperature ranges, although with significant individual temporal and spatial variability in vertical movement patterns, which were also punctuated by stochastic events (e.g., El Niño-Southern Oscillation). Pelagic species can be separated into three broad groups based on daytime temperature preferences by using the unweighted pair-group method with arithmetic averaging clustering on a Kolmogorov-Smirnov Dmax distance matrix: 1) epipelagic species (silky and oceanic whitetip sharks), which spent >95% of their time at temperatures within 2°C of sea surface temperature; 2) mesopelagic-I species (blue sharks and shortfin makos, which spent 95% of their time at temperatures from 9.7° to 26.9°C and from 9.4° to 25.0°C, respectively; and 3) mesopelagic-II species (bigeye threshers), which spent 95% of their time at temperatures from 6.7° to 21.2°C. Distinct thermal niche partitioning based on body size and latitude was also evident within epipelagic species.

Diet composition and prey selection of the introduced grouper species peacock hind (Cephalopholis argus) in Hawaii

The introduced grouper species peacock hind (Cephalopholis argus), was the dominant large-body piscivore on the Main Hawaiian Island (MHI) reefs assessed by underwater visual surveys in this study. However, published data on C. argus feeding ecology are scarce, and the role of this species in Hawaiian reef ecosystems is presently not well understood. Here we provide the first comprehensive assessment of the diet composition, prey electivity (dietary importance of prey taxa compared to their availability on reefs), and size selectivity (prey sizes in the diet compared to sizes on reefs) of this important predator in the MHI. Diet consisted 97.7% of fishes and was characterized by a wide taxonomic breadth. Surprisingly, feeding was not opportunistic, as indicated by a strongly divergent electivity for different prey fishes. In addition, whereas some families of large-body species were represented in the diet exclusively by recruit-size individuals (e.g., Aulostomidae), several families of smaller-body species were also represented by juveniles or adults (e.g., Chaetodontidae). Both the strength and mechanisms of the effects of C. argus predation are therefore likely to differ among prey families. This study provides the basis for a quantitative estimate of prey consumption by C. argus, which would further increase understanding of impacts of this species on native fishes in Hawaii.

Vertical movement patterns of skipjack tuna (Katsuwonus pelamis) in the eastern equatorial Pacific Ocean, as revealed with archival tags

Thirty-three skipjack tuna (Katsuwonus pelamis) (53−73 cm fork length) were caught and released with implanted archival tags in the eastern equatorial Pacific Ocean during April 2004. Six skipjack tuna were recap-tured, and 9.3 to 10.1 days of depth and temperature data were down-loaded from five recovered tags. The vertical habitat-use distributions indicated that skipjack tuna not associated with floating objects spent 98.6% of their time above the thermocline (depth=44 m) during the night, but spent 37.7% of their time below the thermocline during the day. When not associated with floating objects, skipjack tuna displayed repetitive bounce-diving behavior to depths between 50 and 300 m during the day. The deepest dive recorded was 596 m, where the ambient temperature was 7.7°C. One dive was particularly remarkable because the fish contin-uously swam for 2 hours below the thermocline to a maximum depth of 330 m. During that dive, the ambient temperature reached a low of 10.5°C, and the peritoneal cavity temperature reached a low of 15.9°C. The vertical movements and habitat use of skipjack tuna, revealed in this study, provide a much greater understanding of their ecological niche and catchability by purse-seine fisheries.

Multiscale habitat associations of deepwater demersal fishes off central California

Fish-habitat associations were examined at three spatial scales in Monterey Bay, California, to determine how benthic habitats and landscape configuration have structured deepwater demersal fish assemblages. Fish counts and habitat variables were quantified by using observer and video data collected from a submersible. Fish responded to benthic habitats at scales ranging from cm’s to km’s. At broad-scales (km’s), habitat strata classified from acoustic maps were a strong predictor of fish assemblage composition. At intermediate-scales (m’s−100 m’s), fish species were associated with specific substratum patch types. At fine-scales (<1 m), microhabitat associations revealed differing degrees of microhabitat specificity, and for some species revealed niche separation within patches. The use of habitat characteristics in ecosystembased management, particularly as a surrogate for species distributions, will depend on resolving fish-habitat associations and habitat complexity over multiple scales.

Potential for the development of aquaculture in Africa

Aquaculture production in Africa has remained low despite the huge potential that exists on the continent. In order for this potential to be realized, it is necessary to refocus the direction of aquaculture development. This paper concludes that for further growth to occur it is necessary to: (i) widen the range of production systems; (ii) increase production intensities and efficiencies; (iii) develop management technologies for indigenous species that target local niche markets; (iv) put more emphasis on marketing and processing of high value products; (v) promote policy research on how aquaculture production can respond to changing macroeconomic policies; and (vi) accelerate the disengagement of government from activities that can best be done by the private sector.

An Ecological Perspective on Inshore Fisheries in the Main Hawaiian Islands

A description of fisheries within a depth of 100 fathoms is provided for the eight southeastern-most islands of the Hawaiian Archipelago, known as the main Hawaiian Islands (MHI). These are the inhabited islands of the State of Hawaii and are those most subject to inshore fishing pressure, because of their accessibility. Between 1980 and 1990, an average of 1,300 short tons of fishes and invertebrates were reported annually within 100 fm by commercial fishermen. Total landings may be significantly greater, since fishing is a popular pastime of residents and noncommercial landings are not reported. Although limited data are available on noncommercial fisheries, the majority of this review is based on reported commercial landings. The principal ecological factors influencing fisheries in the MHI include coastal currents, the breadth and steepness of the coastal platform, and differences in windward and leeward climate. Expansive coastal development, increased erosion, and sedimentation are among negative human impacts on inshore reef ecosystems on most islands. Commercial fisheries for large pelagics (tunas and billfishes) are important in inshore areas around Ni'ihau, Ka'ula Rock, Kauai, and the Island of Hawaii (the Big Island), as are bottom "handline" fisheries for snappers and groupers around Kauai and Molokai. However, many more inshore fishermen target reef and estuarine species. Two pelagic carangids, "akule," Selar crumenopthalmus, and "opelu," Decapterus macarellus, support the largest inshore fisheries in the MHI. During 1980-90, reported commercial landings within three miles of shore averaged 203 and 125 t for akule and opelu, respectively. Akule landings are distributed fairly evenly throughout the MHI, while more than 72% of the state's inshore opelu landings take place on the Big Island. Besides akule and opelu, other important commercial fisheries on all the MHI include those for surgeon, soldier, parrot, and goatfishes; snappers; octopus, and various trevallies. Trends in reported landings, trips, and catch per unit effort over the last decade are outlined for these fisheries. In heavily populated areas, fishing pressure appears to exceed the capacity of inshore resources to renew themselves. Management measures are beginning to focus on methods of limiting inshore fishing effort, while trying to maintain residents' access to fishing.