Seasonal variation of some trace metal concentrations in some fish species on stretch of River Kubanni, Zaria

In a semi-urbanized stretch of river Kubanni, Zaria, seasonal variations of some tree metals (copper, zinc and lead) in fish species (Clarias sp., Tilapia sp and Alestes sp) were investigated over a period of eight months. Water and fish were sampled monthly, pooled separately and seasonal analysis of each trace determined using atomic absorption method. The concentration of each of the elements in water higher in the dry season than during the rainy season. The dry and rainy season concentrations of copper, zinc and lead were 6.85~c10.66 mu gg super(-1)&1.45~c1.10 mu gg super(-1); 2.13~c1.68 mu gg super(-1)&0.1 5~c0.05 mu gg super(-1); and 0.52~c0.50 mu gg super(-1) & 0.31~c0.14 mu gg super(-1) respectively. Similarly, all the three accumulated more zinc and lead in the dry season than during the rainy season. Tilapia species and to some extent, Alestes species being pelagic had a higher concentration of trace metals than Clarias species which is a bottom dwelling fish Tilapia species may therefore be a better indicator species than Clarias species for monitoring trace metals in water bodies. Reasons for the observed variations in the trace metals were discussed

Fishes associated with pelagic Sargassum and open water lacking Sargassum in the Gulf Stream off North Carolina

The community structure of fishes associated with pelagic Sargassum spp. and open water lacking Sargassum was examined during summer and fall cruises, 1999–2003, in the Gulf Stream off North Carolina. Significantly more individual fishes (n= 18,799), representing at least 80 species, were collected from samples containing Sargassum habitat, compared to 60 species (n=2706 individuals) collected from openwater habitat. The majority (96%) of fishes collected in both habitats were juveniles, and planehead filefish (Stephanolepis hispidus) dominated both habitats. Regardless of sampling time (day or night), Sargassum habitat yielded significantly higher numbers of individuals and species compared with open-water collections. Overall, fishes collected by neuston net tows from Sargassum habitat were significantly larger in length than fishes collected from open-water habitat with neuston nets. A significant positive, linear relationship existed between numbers of fishes and the quantity of Sargassum collected by neuston net. Underwater video recordings indicated a layered structure of fishes among and below the algae and that smaller fishes were more closely associated with the algae than larger fishes. Observations of schooling behaviors of filefishes (Monacanthidae), dolphinfish (Coryphaena hippurus), and jacks (Carangidae), and fish-jellyfish associations were also recorded with an underwater video camera. Our data indicate that Sargassum provides a substantial nursery habitat for many juvenile fishes off the U.S. southeast coast.

Pelagic behavior of adult Greenland halibut (Reinhardtius hippoglossoides)

It is evident from several field experiments with vertical longlines and archival tags, as well as concurrent studies of predator-prey relationships, that adult specimens of the deep-water flatfish Greenland halibut (Reinhardtius hippoglossoides) make regular excursions several hundred meters through the water column. The distribution of longline catches within the water column is confined to a well-defined depth layer overlapping with the distribution of blue whiting (Micromesistius poutassou), an important prey species, and depth recordings from archival tags overlap with Atlantic herring (Clupea harengus), the other major fish prey. The degree of pelagic use varies with fish size as well as seasons. Smaller individuals are found further off the bottom, and pelagic activity is greatest during early autumn. Interaction with pelagic prey species can influence results from bottom trawl surveys.

Age and growth of swordfish (Xiphias gladius) caught by the Hawaii-based pelagic longline fishery

We verified the age and growth of swordfish (Xiphias gla-dius) by comparing ages determined from annuli in fin ray sections with daily growth increments in otoliths. Growth of swordfish of exploitable sizes is described on the basis of annuli present in cross sections of the second ray of the first anal fins of 1292 specimens (60−260 cm eye-to-fork length, EFL) caught in the region of the Hawaii-based pelagic longline fishery. The position of the initial fin ray annulus of swordfish was verified for the first time with the use of scanning electron micrographs of presumed daily growth increments present in the otoliths of juveniles. Fish growth through age 7 was validated by marginal increment analysis. Faster growth of females was confirmed, and the standard von Bertalanffy growth model was identified as the most parsimonious for describing growth in length for fish greater than 60 cm EFL. The observed growth of three fish, a year-old in size when first caught and then recaptured from 364 to1490 days later, is consistent with modeled growth for fish of this size range. Our novel approach to verifying age and growth should increase confidence in conducting an age-structured stock assessment for swordfish in the North Pacific Ocean.

Survival of white marlin (Tetrapturus albidus) released from commercial pelagic longline gear in the western North Atlantic

To estimate postrelease survival of white marlin (Tetrapturus albidus) caught incidentally in regular commercial pelagic longline fishing operations targeting swordfish and tunas, short-duration popup satellite archival tags (PSATs) were deployed on captured animals for periods of 5−43 days. Twenty (71.4%) of 28 tags transmitted data at the preprogrammed time, including one tag that separated from the fish shortly after release and was omitted from subsequent analyses. Transmitted data from 17 of 19 tags were consistent with survival of those animals for the duration of the tag deployment. Postrelease survival estimates ranged from 63.0% (assuming all nontransmitting tags were evidence of mortality) to 89.5% (excluding nontransmitting tags from the analysis). These results indicate that white marlin can survive the trauma resulting from interaction with pelagic longline gear, and indicate that current domestic and international management measures requiring the release of live white marlin from this fishery will reduce fishing mortality on the Atlantic-wide stock.

Diet composition and food habits of demersal and pelagic marine fishes from Terengganu waters, east coast of Peninsular Malaysia

Fish stomachs from 18 demersal and pelagic fishes from the coast of Terengganu in Malaysia were examined. The components of the fishes’ diets varied in number, weight, and their frequency of occurrence. The major food items in the stomachs of each species were determined using an Index of Relative Importance. A conceptual food web structure indicates that fish species in the study area can be classified into three predatory groups: (1) predators on largely planktivorous or pelagic species; (2) predators on largely benthophagous or demersal species; and (3) mixed feeders that consume both pelagic and demersal species.

A program for the identification of the pelagic eggs of Black Sea fishes

A computer program was developed for the identification of the teleost fish eggs that may be found in the pelagic zone of the Black Sea. The program identifies eggs of 70 species, using up to 28 descriptive characters, and may be adapted for use outside of the Black Sea.

Atlantic Blue Marlin, Makaira nigricans, and White Marlin, Tetrapterus albidus, Bycatch of the Japanese Pelagic Longline Fishery, 1960–2000

ABSTRACT—Since the late 1950’s, a multi-national longline fishery has operated throughout the Atlantic Ocean to supply the growing global demand for tunas (Scombridae) and swordfish, Xiphias gladius. Two species caught as bycatch include Atlantic blue marlin, Makaira nigricans, and white marlin, Tetrapterus albidus, referred to in this paper as “Atlantic marlin.” Pelagic longlining has consistently been the principal source of adult mortality for both species, which are currently depleted and have been so for more than two decades. In this paper, we examined aspects of the Atlantic marlin bycatch of the Japanese pelagic longline fishery from 1960 to 2000. Temporal and spatial patterns in effort, target catch (species combined), marlin bycatch, marlin catch-per-unit-effort (nominal CPUE), and ratios of marlin bycatch to target catch (B: T ratios) were analyzed. An objective was to reveal changes, if any, in marlin bycatch associated with the fishery’s target species “switch” (ca. 1980–87) from mostly surface-associated tunas to mostly the deeper-dwelling bigeye tuna, Thunnus obesus. The highest values of all variables examined occurred during the 1960’s and then fell by the second half of that decade. Since 1970, mean levels of fishing effort, target fish catches, and blue marlin landings have increased significantly, while blue marlin CPUE and B:T ratios have remained relatively stable. Concurrently, white marlin landings, CPUE, and B:T ratios have all declined. While results suggest the fishery’s target species change may have been a factor in lowering white marlin bycatch, the same cannot be said for blue marlin. Relative increases in blue marlin B:T ratios off the northeastern coast of South America and in the wider eastern Atlantic are cause for concern, as are continuing trends of CPUE decline for white marlin in this data set as well as others.

Reported Trip Costs, Gross Revenues, and Net Returns for U.S. Atlantic Pelagic Longline Vessels

Logbook set and trip summary data (containing catch and cost information, respectively) collected by NOAA’s National Marine Fisheries Service (NMFS) were analyzed for U.S. pelagic longline vessels that participated in Atlantic fisheries in 1996. These data were augmented with vessel information from the U.S. Coast Guard. Mean fish weights and ex-vessel prices from NMFS observers and licensed seafood dealers, respectively, were used to estimate gross revenues. Comparisons revealed that net returns varied substantially by vessel size and fishing behavior (i.e. sets per trip, fishing location, season, and swordfish targeting). While the calculated economic effects of proposed regulations will depend on the descriptive statistic chosen for analysis, which itself depends on the type of analysis being conducted, results show that considering heterogeneity within this fleet can have a significant effect on predicted economic consequences.

Review of a Small-scale Pelagic Longline Fishery off Northeastern Brazil

The annual catches of four small longliners operating off northeast Brazil from 1983 to 1997 were examined across different areas and locations. The total catch comprised tunas (30%), sharks (54%), billfishes (12%), and other fish species (4%). Fishing strategy and annual composition of catches showed large spatial and temporal variabilities with the dominant catches alternating among yellowfin tuna, Thunnus albacares; gray sharks, Carcharhinus spp.; and blue shark, Prionace glauca. Catches of blue and gray sharks showed a significant interaction among seamounts, with gray sharks occurring in maximum abundance around those seamounts that had relatively deep summits and low-sloping depth profiles. Results are discussed in terms of the various factors that may have influenced distribution of effort.

Recent Trends in the Catch of Undersized Swordfish by the U.S. Pelagic Longline Fishery

U.S. commercial vessels fishing in the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico have been subject to regulations limiting the landing of swordfish less than 25 kg whole weight since June 1991. The intent of those regulations was to reduce the mortality of immature swordfihs. Plots of fishing effort from 1990 to 1994 indicate that the regulations were effective in some areas. Fishing effort decreased after 1991 in the Venezuelan Basin, a swordfish nursery area. However, in areas close to the U.S. coastline, effort did not appear to shift away from areas where immature swordfish were discarded. To identify areas with high rates of discarding, plots were made showing areas where the number of discarded swordfish was equal to or greater than the number of fish landed.

Survey Assessment of Semi-pelagic Gadoids: The Example of Walleye Pollock, Theragra chalcogramma, in the Eastern Bering Sea

Assessment of walleye pollock, Theragra chalcogramma, in the eastern Bering Sea is complicated because the species is semi-pelagic in habit. Annual bottom trawl surveys provide estimates of demersal abundance on the eastern Bering Sea shelf. Every third year (starting in 1979), an extended area of the shelf and slope is surveyed and an echo integration-midwater trawl survey provides estimates of pollock abundance in midwater. Overall age-specific population and biomass estimates are obtained by summing the demersal and midwater results, assuming that the bottom trawl samples only pollock inhabiting the lower 3 m of the water column. Total population estimates have ranged from 134 x 109 fish in 1979 to 27 x 109 fish in 1988. The very high abundance observed in 1979 reflects the appearance of the unusually large 1978 year class. Changes in age-specific abundance estimates have documented the passage of strong (1978, 1982, and 1984) and weak year classes through the fishery. In general, older fish are more demersally oriented and younger fish are more abundant in midwater, but this trend was not always evident in the patterns of abundance of 1- and 2-year-old fish. As the average age of the population has increased, so has the relative proportion of pollock estimated by the demersal surveys. Consequently, it is unlikely that either technique can be used independently to monitor changes in abundance and age composition. Midwater assessment depends on pelagic trawl samples for size and age composition estimates, so both surveys are subject to biases resulting from gear performance and interactions between fish and gear. In this review, we discuss survey methodology and evaluate assumptions regarding catchability and availability as they relate to demersal, midwater, and overall assessment.

Hawaii's Pelagic Fisheries

Hawaii's diverse pelagic fisheries supply the bulk of the State's total catch. The largest Hawaii fishery is the recently expanded longline fishery, which now lands about 4,400 metric tons (t) of broadbill swordfish, Xiphias gladius; 1,500 t of bigeye tuna, Thunnus obesus, and 3,000 t of other pelagic species annually. The increased catch of these other species has raised concerns regarding the continued availability of yellowfin tuna, T. albacares; blue marlin, Makaira mazara; and mahimahi, Coryphaena hippurus, in the small-vessel troll and handline fisheries which target those species. Analysis of catch per unit effort (CPUE) statistics from Hawaii's fisheries did not provide strong evidence of recent declines in availability related to local fishery expansion. A more influential factor was variation in Pacific-wide CPUE, representing overall population abundance and catchability. Exogenous factors, including Pacific-wide fishing pressure, may overwhelm the influence of local fishing pressure on fish availability.

Effects of the Santa Barbara, Calif., Oil Spill on the Apparent Abundance of Pelagic Fishery Resources

Many studies have been made of the effects of oil on marine invertebrates, plants (marine algae and phytoplankton), and vertebrates such as seabirds and marine mammals. An excellent review of these findings, which includes some references to fish and pathological effects of aromatic hydrocarbons, has been published by the Royal Society, London (Clark, 1982). That review dealt with the environmental effects of such major oil spills or releases such as those by the tankers Torry Canyon (119,000 t) on the south coast of England, Metula (50-56,000 t) in the Straits of Magellan, Argo Merchant (26,000 t) off Cape Cod, and the super tanker Amoco Cadiz (223,000 t) on the coast of northern Brittany. Those spills were studied to determine their effect on living resources. In contrast there are few references on the impact of oil spills on pelagic fishery resources.

Food habits of Sowerby's beaked whales (Mesoplodon bidens) taken in the pelagic drift gillnet fishery of the western North Atlantic

We describe the food habits of the Sowerby’s beaked whale (Mesoplodon bidens) from observations of 10 individuals taken as bycatch in the pelagic drift gillnet fishery for Swordfish (Xiphias gladius) in the western North Atlantic and 1 stranded individual from Kennebunk, Maine. The stomachs of 8 bycaught whales were intact and contained prey. The diet of these 8 whales was dominated by meso- and benthopelagic fishes that composed 98.5% of the prey items found in their stomachs and cephalopods that accounted for only 1.5% of the number of prey. Otoliths and jaws representing at least 31 fish taxa from 15 families were present in the stomach contents. Fishes, primarily from the families Moridae (37.9% of prey), Myctophidae (22.9%), Macrouridae (11.2%), and Phycidae (7.2%), were present in all 8 stomachs. Most prey were from 5 fish taxa: Shortbeard Codling (Laemonema barbatulum) accounted for 35.3% of otoliths, Cocco’s Lanternfish (Lobianchia gemellarii) contributed 12.9%, Marlin-spike (Nezumia bairdii) composed 10.8%, lanternfishes (Lampanyctus spp.) accounted for 8.4%; and Longfin Hake (Phycis chesteri) contributed 6.7%. The mean number of otoliths per stomach was 1196 (range: 327–3452). Most of the fish prey found in the stomachs was quite small, ranging in length from 4.0 to 27.7 cm. We conclude that the Sowerby’s beaked whales that we examined in this study fed on large numbers of relatively small meso- and benthopelagic fishes that are abundant along the slope and shelf break of the western North Atlantic.