Reproductive biology of blue marlin (Makaira nigricans) in the western Pacific Ocean

The reproductive biology of blue marlin (Makaira nigricans) was assessed from 1001 fish (ranging from 121 to 275 cm in eye-to-fork length; EFL) caught by Taiwanese offshore longliners in the western Pacific Ocean from September 2000 to December 2001 and from 843 gonad samples from these fish, The overall sex ratio of the catch was approximately 1:1 dur ing the sampling period, but blue marlin are sexually dimorphic; females are larger than males. Reproductive activity (assessed by histology), a gonadosomatic index, and the distribution of oocyte diameters, indicated that spawning occurred predominantly from May to September. The estimated sizes-at-maturity (EFL50) were 179.76 ±1.01 cm (mean ±standard error) for females and 130 ±1 cm EFL for males. Blue marlin are multiple spawners and oocytes develop asynchronously. The proportion of mature females with ovaries containing postovulatory follicles (0.41) and hydrated oocytes (0.34) indicated that the blue marlin spawned once every 2–3 days on average. Batch fecundity (BF) for 26 females with the most advanced oocytes (≥1000 μm), but without postovulatory follicles, ranged from 2.11 to 13.50 million eggs (6.94 ± 0.54 million eggs). The relationships between batch fecundity (BF, in millions of eggs) and EFL and round weight (RW, kg) were BF = 3.29 × 10 –12 EFL5.31 (r2 = 0.70) and BF = 1.59 × 10–3 RW 1.73 (r2= 0.67), respectively. The parameters estimated in this study are key information for stock assessments of blue marlin in the western Pacific Ocean and will contribute to the conservation and sustainable yield of

Abundance, condition, and diet of juvenile Pacific ocean perch (Sebastes alutus) in the Aleutian Islands

T he relative value of pelagic habitat for three size classes of juvenile Pacific ocean perch (Sebastes alutus) was investigated by comparing their abundance and condition in two areas of the Aleutian Islands. Diet, zooplankton biomass, and water column temperatures were examined as potential factors affecting observed differences. Juvenile Pacific ocean perch abundance and condition, and zooplankton biomass varied significantly between areas, whereas juvenile Pacific ocean perch diet varied only by size class. Observed differences in fish condition may have been due to the quantity or quality of pelagic prey items consumed. For the delineation of essential demersal fish habitat, important ecological features of the pelagic habitat must therefore be considered.

Recalculated diet and daily ration of the shortfin mako (Isurus oxyrinchus), with a focus on quantifying predation on bluefish (Pomatomus saltatrix) in the northwest Atlantic Ocean

The diet and daily ration of the shortfin mako (Isurus oxyrinchus) in the northwest Atlantic were re-examined to determine whether fluctuations in prey abundance and availability are reflected in these two biological variables. During the summers of 2001 and 2002, stomach content data were collected from fishing tournaments along the northeast coast of the United States. These data were quantified by using four diet indices and were compared to index calculations from historical diet data collected from 1972 through 1983. Bluefish (Pomatomus saltatrix) were the predominant prey in the 1972–83 and 2001–02 diets, accounting for 92.6% of the current diet by weight and 86.9% of the historical diet by volume. From the 2001– 02 diet data, daily ration was estimated and it indicated that shortfin makos must consume roughly 4.6% of their body weight per day to fulfill energetic demands. The daily energetic requirement was broken down by using a calculated energy content for the current diet of 4909 KJ/kg. Based on the proportional energy of bluefish in the diet by weight, an average shortfin mako consumes roughly 500 kg of bluefish per year off the northeast coast of the United States. The results are discussed in relation to the potential effect of intense shortfin mako predation on bluefish abundance in the region.

Prevalence of the commensal barnacle Xenobalanus globicipitis on cetacean species in the eastern tropical Pacific Ocean, and a review of global occurrence

Distribution and prevalence of the phoretic barnacle Xenobalanus on cetacean species are reported for 22 cetaceans in the eastern tropical Pacific Ocean (21 million km2). Four cetacean species are newly reported hosts for Xenobalanus: Bryde’s whale (Balaenoptera edeni), long-beaked common dolphin (Delphinus capensis), humpback whale (Megaptera novaeangliae), and spinner dolphin (Stenella longirostris). Sightings of Xenobalanus in pelagic waters are reported for the first time, and concentrations were located within three productive zones: near the Baja California peninsula, the Costa Rica Dome and waters extending west along the 10°N Thermocline Ridge, and near Peru and the Galapagos Archipelago. Greatest prevalence was observed on blue whales (Balaenoptera musculus) indicating that slow swim speeds are not necessary for effective barnacle settlement. Overall, prevalence and prevalence per sighting were generally lower than previously reported. The number of barnacles present on an individual whale was greatest for killer whales, indicating that Xenobalanus larvae may be patchily distributed. The broad geographic distribution and large number of cetacean hosts, indicate an extremely cosmopolitan distribution. A better understanding of the biology of Xenobalanus is needed before this species can be used as a biological tag.

Catches in ghost-fishing octopus and fish traps in the northeastern Atlantic Ocean (Algarve, Portugal)

Ghost fishing is the term used to describe the continued capture of fish and other living organisms after a fisherman has lost all control over the gear. Traps may be lost for a variety of reasons including theft, vandalism, abandonment, interactions with other gear, fouling on the bottom (i.e., traps and ropes are caught on rocky substrate), bad weather, and human error (Laist, 1995). Annual trap loss can be as high as 20% to 50% of fished traps in some fisheries (Al-Masroori et al., 2004). Because lost traps can continue to fish for long periods, albeit with decreasing efficiency over time (e.g., Smolowitz, 1978; Breen, 1987, 1990; Guillory, 1993), ghost fishing is a concern in fisheries worldwide.

An ecological analysis of rockfish (Sebastes spp.) assemblages in the North Pacific Ocean along broad-scale environmental gradients

Environmental variability affects the distributions of most marine fish species. In this analysis, assemblages of rockfish (Sebastes spp.) species were defined on the basis of similarities in their distributions along environmental gradients. Data from 14 bottom trawl surveys of the Gulf of Alaska and Aleutian Islands (n=6767) were used. Five distinct assemblages of rockfish were defined by geographical position, depth, and temperature. The 180-m and 275-m depth contours were major divisions between assemblages inhabiting the shelf, shelf break, and lower continental slope. Another noticeable division was between species centered in southeastern Alaska and those found in the northern Gulf of Alaska and Aleutian Islands. The use of environmental variables to define the species composition of assemblages is different from the use of traditional methods based on clustering and nonparametric statistics and as such, environmentally based analyses should result in predictable assemblages of species that are useful for ecosystem-based management.

Timing and duration of mating and brooding periods of Atka mackerel (Pleurogrammus monopterygius) in the North Pacific Ocean

The timing and duration of the reproductive cycle of Atka mackerel (Pleurogrammus monopterygius) was validated by using observations from time-lapse video and data from archival tags, and the start, peak, and end of spawning and hatching were determined from an incubation model with aged egg samples and empirical incubation times ranging from 44 days at a water temperature of 9.85°C to 100 days at 3.89°C. From June to July, males ceased diel vertical movements, aggregated in nesting colonies, and established territories. Spawning began in late July, ended in mid-October, and peaked in early September. The male egg-brooding period that followed continued from late November to mid-January and duration was highly dependent on embryonic development as affected by ambient water temperature. Males exhibited brooding behavior for protracted periods at water depths from 23 to 117 m where average daily water temperatures ranged from 4.0° to 6.2°C. Knowledge about the timing of the reproductive cycle provides a framework for conserving Atka mackerel populations and investigating the physical and biological processes influencing recruitment.

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.

Interactions between marine mammals and pelagic longline fishing gear in the U.S. Atlantic Ocean between 1992 and 2004

The U.S. East Coast pelagic longline fishery has a history of interactions with marine mammals, where animals are hooked and entangled in longline gear. Pilot whales (Globicephala spp.) and Risso’s dolphin (Grampus griseus) are the primary species that interact with longline gear. Logistic regression was used to assess the environmental and gear characteristics that influence interaction rates. Pilot whale inter-actions were correlated with warm water temperatures, proximity to the shelf break, mainline lengths greater than 20 nautical miles, and damage to swordfish catch. Similarly, Risso’s dolphin interactions were correlated with geographic location, proximity the shelf break, the length of the mainline, and bait type. The incidental bycatch of marine mammals is likely associated with depredation of the commercial catch and is increased by the overlap between marine mammal and target species habitats. Altering gear characteristics and fishery practices may mitigate incidental bycatch and reduce economic losses due to depredation.

Natural mortality rate, annual fecundity, and maturity at length for Greenland halibut (Reinhardtius hippoglossoides) from the northeastern Pacific Ocean

Mortality, fecundity, and size at maturity are important life history traits, and their interactions determine the evolution of life history strategies (Roff, 1992; Stearns, 1992; Charnov, 2002). These same traits are also important for population dynamics models (Hunter et al., 1992; Clark, 1999). It is increasingly important to accurately determine Greenland halibut (Reinhardtius hippoglossoides) life history traits and to correctly assess the status of its stocks because low recruitment or low biomass estimates have led to catch restrictions in the Bering Sea and Aleutian Islands (Ianelli et al.1), the Northeastern Arctic (Ådlandsvik et al., 2004), and the Northwest Atlantic (Bowering and Nedreaas, 2000).

The potential use of time-area closures to reduce catches of bigeye tuna (Thunnus obesus) in the purse-seine fishery of the eastern Pacific Ocean

Skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye (Thunnus obesus) tunas are caught by purse-seine vessels in the eastern Pacific Ocean (EPO). Although there is no evidence to indicate that current levels of fishing-induced mortality will affect the sustainability of skipjack or yellowfin tunas, fishing mortality on juvenile (younger than 5 years of age) bigeye tuna has increased, and overall fishing mortality is greater than that necessary to produce the maximum sustainable yield of this species. We investigated whether time-area closures have the potential to reduce purse-seine bigeye catches without significantly reducing skipjack catches. Using catch and effort data for 1995–2002, we identified regions where the ratio of bigeye to skipjack tuna catches was high and applied simple closed-area models to investigate the possible benefits of time-area closures. We estimated that the most optimistic and operationally feasible 3-month closures, covering the equatorial region of the EPO during the third quarter of the year, could reduce bigeye catches by 11.5%, while reducing skipjack tuna catches by 4.3%. Because this level of bigeye tuna catch reduction is insufficient to address sustainability concerns, and larger and longer closures would reduce catches of this species signficantly, we recommend that future research be directed toward gear technology solutions because these have been successful in many other fisheries. In particular, because over 50% of purse-seine catches of bigeye tuna are taken in sets in which bigeye tuna are the dominant species, methods to allow the determination of the species composition of aggregations around floating objects may be important.

Use of genetic data to assess the uncertainty in stock assessments due to the assumed stock structure: the case of albacore (Thunnus alalunga) from the Atlantic Ocean

Stock assessments can be problematic because of uncertainties associated with the data or because of simplified assumptions made when modeling biological processes (Rosenberg and Restrepo, 1995). For example, the common assumption in stock assessments that stocks are homogeneous and discrete (i.e., there is no migration between the stocks) is not necessarily true (Kell et al., 2004a, 2004b).

New information from fish diets on the importance of glassy flying squid (Hyaloteuthis pelagica) (Teuthoidea: Ommastrephidae) in the epipelagic cephalopod community of the tropical Atlantic Ocean

Squids of the family Ommastrephidae are a vital part of marine food webs and support major fisheries around the world. They are widely distributed in the open ocean, where they are among the most abundant in number and biomass of nektonic epipelagic organisms. In turn, seven of the 11 genera of this family (Dosidicus, Illex, Martialia, Nototodarus, Ommastrephes, Sthenoteuthis, and Todarodes) are heavily preyed upon by top marine predators, i.e., birds, mammals, and fish, and currently support fisheries in both neritic and oceanic waters (Roper and Sweeney, 1984; Rodhouse, 1997). Their commercial importance has made the large ommastrephids the target of many scientific investigations and their biology is consequently reasonably well-known (Nigmatullin et al., 2001; Zuyev et al., 2002; Bower and Ichii, 2005). In contrast, much less information is available on the biology and ecological role of the smaller, unexploited species of ommastrephids (e.g., Eucleoteuthis, Hyaloteuthis, Ornithoteuthis, and Todaropsis).

Interdecadal change in growth of sablefish (Anoplopoma fimbria) in the northeast Pacific Ocean

Errors in growth estimates can affect drastically the spawner-perrecruit threshold used to recommend quotas for commercial fish catches. Growth parameters for sablefish (Anoplopoma fimbria) in Alaska have not been updated for stock assessment purposes for more than 20 years, although aging of sablefish has continued. In this study, length-stratified data (1981–93 data from the annual longline survey conducted cooperatively by the Fisheries Agency of Japan and the Alaska Fisheries Science Center of the National Marine Fisheries Service) were updated and corrected for discovered sampling bias. In addition, more recent, randomly collected samples (1996–2004 data from the annual longline survey conducted by the Alaska Fisheries Science Center) were analyzed and new length-at-age and weight-at-age parameters were estimated. Results were similar between this analysis with length-at-age data from 1981 to 2004 and analysis with updated longline survey data through 2010; therefore, we used our initial results from analysis done with data through 2004. We found that, because of a stratified sampling scheme, growth estimates of sablefish were overestimated with the older data (1981–93), and growth parameters used in the Alaskan sablefish assessment model were, thus, too large. In addition, a comparison of the bias-corrected 1981–93 data and the 1996–2004 data showed that, in more recent years, sablefish grew larger and growth differed among regions. The updated growth information improves the fit of the data to the sablefish stock assessment model with biologically reasonable results. These findings indicate that when the updated growth data (1996–2004) are used in the existing sablefish assessment model, estimates of fishing mortality increase slightly and estimates of female spawning biomass decrease slightly. This study provides evidence of the importance of periodically revisiting biological parameter estimates, especially as data accumulate, because the addition of more recent data often will be more biologically realistic. In addition, it exemplifies the importance of correcting biases from sampling that may contribute to erroneous parameter estimates.

Toward identification of larval sailfish (Istiophorus platypterus), white marlin (Tetrapturus albidus), and blue marlin (Makaira nigricans) in the western North Atlantic Ocean*

The identification of larval istiophorid billfishes from the western North Atlantic Ocean has long been problematic. In the present study, a molecular technique was used to positively identify 27 larval white marlin (Tetrapturus albidus), 96 larval blue marlin (Makaira nigricans), and 591 larval sailfish (Istiophorus platypterus) from the Straits of Florida and the Bahamas. Nine morphometric measurements were taken for a subset of larvae (species known), and lower jaw pigment patterns were recorded on a grid. Canonical variates analysis (CVA) was used to reveal the extent to which the combination of morphometric, pigment pattern, and month of capture information was diagnostic to species level. Linear regression revealed species-specific relationships between the ratio of snout length to eye orbit diameter and standard length (SL). Confidence limits about these relationships served as defining characters for sailfish >10 mm SL and for blue and white marlin >17 mm SL. Pigment pattern analysis indicated that 40% of the preflexion blue marlin examined possessed a characteristic lower jaw pigment pattern and that 62% of sailfish larvae were identifiable by lower jaw pigments alone. An identification key was constructed based on pigment patterns, month of capture, and relationships between SL and the ratio of snout length to eye orbit diameter. The key yielded identifications for 69.4% of 304 (blind sample) larvae used to test it; only one of these identifications was incorrect. Of the 93 larvae that could not be identified by the key, 71 (76.3%) were correctly identified with CVA. Although identif ication of certain larval specimens may always require molecular techniques, it is encouraging that the majority (92.4%) of istiophorid larvae examined were ultimately identifiable from external characteristics alone.