Variations in eastern North Pacific demersal fish biomass based on the U.S. west coast groundfish bottom trawl survey (2003–2010)

In response to declining biomass of Northeast Pacific groundfish in the late 1990s and to improve the scientific basis for management of the fishery, the Northwest Fisheries Science Center standardized and enhanced their annual bottom trawl survey in 2003. The survey was expanded to include the entire area along the U.S. west coast at depths of 55–1280 m. Coast-wide biomass and species richness significantly decreased during the first eight years (2003–10) of this fishery-independent survey. We observed an overall tendency toward declining biomass for 62 dominant taxa combined (fishery target and nontarget species) and four of seven subgroups (including cartilaginous fish, flatfishes, shelf rockfishes, and other shelf species), despite increasing or variable biomass trends in individual species. These decreases occurred during a period of reduced catch for groundfish along the shelf and upper slope regions relative to historical rates. We used information from multiple stock assessments to aggregate species into three groups: 1) with strong recruitment, 2) without strong recruitment in 1999, and 3) with unknown recruitment level. For each group, we evaluated whether declining biomass was primarily related to depletion (using year as a proxy) or environmental factors (i.e., variation in the Pacific Decadal Oscillation). According to Akaike’s information criterion, changes in aggregate biomass for species with strong recruitment were more closely related to year, whereas those with no strong recruitment were more closely related to climate. The significant decline in biomass for species without strong recruitment confirms that factors other than depletion of the exceptional 1999 year class may be responsible for the observed decrease in biomass along the U.S. west coast.

Comparative feeding ecology of two elasmobranch species, Squalus blainville and Scyliorhinus canicula, off the coast of Portugal

The small-spotted catshark (Scyliorhinus canicula) (Linnaeus, 1758) and the longnose spurdog (Squalus blainville) (Risso, 1826) are two species occurring in the European and western African continental shelves with a wide geographical distribution. In this study, the diet of S. blainville and S. canicula off the Portuguese western Atlantic coast was investigated in 2006 by collecting monthly samples of these two species from local fishing vessels. In the stomachs of both species, crustaceans and teleosts were the dominant prey items, and molluscs, polychaetes, echinoderms, and sipunculids were found in lower abundance. In S. canicula, urochordate and chondrichthyan species were also observed in stomachs and were classified as accidental prey items. Scyliorhinus canicula consumed a broader group of prey items than did S. blainville. A significant diet overlap was observed, despite both species occupying different depth ranges over the continental shelf. Scyliorhinus canicula exhibited a consistency in diet composition among seasons, sexes, and maturity stages. Nonetheless, for both adults and juveniles, an increase in relative abundance of teleosts in the diet was observed in the spring and summer. This study provides evidence of the importance of S. canicula and S. blainville as benthic and pelagic predators along the western Atlantic coast.

Otolith morphometrics and population structure of Pacific sardine (Sardinops sagax) along the west coast of North America

The broad distribution of Pacific sardine (Sardinops sagax) along the Pacif ic coast of North America makes it difficult for fisheries managers to identify regional stocks of this dominant small pelagic species. An investigation of morphometric characteristics of otoliths of Pacific sardine across most of their range revealed regional differences in populations. In a survey of over 2000 otoliths, all ages (with an emphasis on age-1 recruits) were compared. Principal components analysis, multivariate analysis of variance, and a novel method derived from regression and residuals calculations, termed perimeter-weight profiles (PWPs), revealed otolith similarities and differences. The results of the different approaches to statistical comparisons did not always agree. Sardine otoliths from Mexican waters were generally lighter and more lobate than those from U.S. and Canadian populations. Age-1 otoliths from northern California in 2006–07 tended to be heavier and smoother than those from other areas, including year-class cohorts from southern California. Comparisons of age-groups and year-classes of northern California otoliths with the use of the PWP models indicated signif icant trends in year-to-year patterns. In conjunction with other established indices of population structure, otolith PWPs are a useful tool for identifying local and regional stocks of Pacific sardine and may help distinguish populations of other fish species as well.

Ocean distribution of the American shad (Alosa sapidissima) along the Pacific coast of North America

We examined the incidental catches of American shad (Alosa sapidissima) taken during research cruises and in commercial and recreational landings along the Pacific coast of North America during over 30 years of sampling. Shad, an introduced species, was mainly found over the shallow continental shelf, and largest catches and highest frequency of occurrences were found north of central Oregon, along the coasts of Washington and Vancouver Island, and in California around San Francisco Bay. Migrations to the north off Washington and Vancouver were seen during spring to fall, but we found no evidence for large-scale seasonal migrations to the south during the fall or winter. The average weight of shad increased in deeper water. Sizes were also larger in early years of the study. Most were caught over a wide range of sea surface temperatures (11–17°C) and bottom temperatures (6.4–8.0°C). Abundance of shad on the continental shelf north of 44°N was highly correlated with counts of shad at Bonneville Dam on the Columbia River in the same year. Counts were negatively related to average weights and also negatively correlated with the survival of hatchery coho salmon (Oncorhynchus kisutch), indicating that survival of shad is favored by warm ocean conditions. Examining the catch during research cruises and commercial and recreational landings, we concluded that American shad along the Pacific coast have adapted to the prevailing environmental conditions and undertake only moderate seasonal migrations compared with the long seasonal migrations of shad along the Atlantic coast of North America. We suggest that the large spawning populations in the Columbia River and San Francisco Bay areas explain most of the distributional features along the Pacific coast.

Season- and depth-dependent variability of a demersal fish assemblage in a large fjord estuary (Puget Sound, Washington)

Fjord estuaries are common along the northeast Pacific coastline, but little information is available on fish assemblage structure and its spatiotemporal variability. Here, we examined changes in diversity metrics, species biomasses, and biomass spectra (the distribution of biomass across body size classes) over three seasons (fall, winter, summer) and at multiple depths (20 to 160 m) in Puget Sound, Washington, a deep and highly urbanized fjord estuary on the U.S. west coast. Our results indicate that this fish assemblage is dominated by cartilaginous species (spotted ratfish [Hydrolagus colliei] and spiny dogfish [Squalus acanthias]) and therefore differs fundamentally from fish assemblages found in shallower estuaries in the northeast Pacific. Diversity was greatest in shallow waters (<40 m), where the assemblage was composed primarily of flatfishes and sculpins, and lowest in deep waters (>80 m) that are more common in Puget Sound and that are dominated by spotted ratf ish and seasonally (fall and summer) by spiny dogfish. Strong depth-dependent variation in the demersal fish assemblage may be a general feature of deep fjord estuaries and indicates pronounced spatial variability in the food web. Future comparisons with less impacted fjords may offer insight into whether cartilaginous species naturally dominate these systems or only do so under conditions related to human-caused ecosystem degradation. Information on species distributions is critical for marine spatial planning and for modeling energy flows in coastal food webs. The data presented here will aid these endeavors and highlight areas for future research in this important yet understudied system.

Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa

This study documents validation of vertebral band-pair formation in spotted gully shark (Triakis megalopterus) with the use of fluorochrome injection and tagging of captive and wild sharks over a 21-year period. Growth and mortality rates of T. megalopterus were also estimated and a demographic analysis of the species was conducted. Of the 23 OTC (oxytetracycline) -marked vertebrae examined (12 from captive and 11 from wild sharks), seven vertebrae (three from captive and four from wild sharks) exhibited chelation of the OTC and fluoresced under ultraviolet light. It was concluded that a single opaque and translucent band pair was deposited annually up to at least 25 years of age, the maximum age recorded. Reader precision was assessed by using an index of average percent error calculated at 5%. No significant differences were found between male and female growth patterns (P>0.05), and von Bertalanffy growth model parameters for combined sexes were estimated to be L∞=1711.07 mm TL, k=0.11/yr and t0=–2.43 yr (n=86). Natural mortality was estimated at 0.17/yr. Age at maturity was estimated at 11 years for males and 15 years for females. Results of the demographic analysis showed that the population, in the absence of fishing mortality, was stable and not significantly different from zero and particularly sensitive to overfishing. At the current age at first capture and natural mortality rate, the fishing mortality rate required to result in negative population growth was low at F>0.004/ yr. Elasticity analysis revealed that juvenile survival was the principal factor in explaining variability in population growth rate.

Food habits of Atlantic white-sided dolphins (Lagenorhynchus acutus) off the coast of New England

Although the Atlantic white-sided dolphin (Lagenorhynchus acutus) is one of the most common dolphins off New England, little has been documented about its diet in the western North Atlantic Ocean. Current federal protection of marine mammals limits the supply of animals for investigation to those incidentally caught in the nets of commercial fishermen with observers aboard. Stomachs of 62 L. acutus were examined; of these 62 individuals, 28 of them were caught by net and 34 were animals stranded on Cape Cod. Most of the net-caught L. acutus were from the deeper waters of the Gulf of Maine. A single stomach was from the continental slope south of Georges Bank. At least twenty-six fish species and three cephalopod species were eaten. The predominant prey were silver hake (Merluccius bilinearis), spoonarm octopus (Bathypolypus bairdii), and haddock (Melanogrammus aeglefinus). The stomach from a net-caught L. acutus on the continental slope contained 7750 otoliths of the Madeira lanternfish (Ceratoscopelus maderensis). Sand lances (Ammodytes spp.) were the most abundant (541 otoliths) species in the stomachs of stranded L. acutus. Seasonal variation in diet was indicated; pelagic Atlantic herring (Clupea harengus) was the most important prey in summer, but was rare in winter. The average length of fish prey was approximately 200 mm, and the average mantle length of cephalopod prey was approximately 50 mm.

Spatial and seasonal abundance of sand seatrout (Cynoscion arenarius) and silver seatrout (C. nothus) off the coast of Texas, determined with twenty years of data (1987–200

Sand seatrout (Cynoscion arenarius) and silver seatrout (C. nothus) are both found within the immediate offshore areas of the Gulf of Mexico, especially around Texas; however information is limited on how much distributional overlap really occurs between these species. In order to investigate spatial and seasonal differences between species, we analyzed twenty years of bay and offshore trawl data collected by biologists of the Coastal Fisheries Division, Texas Parks and Wildlife Department. Sand seatrout and silver seatrout were distributed differently among offshore sampling areas, and salinity and water depth appeared to correlate with their distribution. Additionally, within the northernmost sampling area of the gulf waters, water depth correlated significantly with the presence of silver seatrout, which were found at deeper depths than sand seatrout. There was also an overall significant decrease in silver seatrout abundance during the summer season, when temperatures were at their highest, and this decrease may have indicated a migration farther offshore. Sand seatrout abundance had an inverse relationship with salinity and water depth offshore. In addition, sand seatrout abundance was highest in bays with direct passes to the gulf and correlated with corresponding abundance in offshore areas. These data highlight the seasonal and spatial differences in abundance between sand and silver seatrout and relate these differences to the hydrological and geological features found along the Texas coastline.

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.

Mitochondrial DNA markers to identify commercial spiny lobster species (Panulirus spp.) from the Pacific coast of Mexico: an application on phyllosoma larvae

Molecular markers based on mitochondrial DNA (mtDNA) are extensively used to study genetic relationships. mtDNA has been used in phylogenetic studies to understand the evolutionary history of species because it is maternally inherited and is not subject to genetic recombination (Gyllensten et al., 1991). The high mutation rate of mtDNA makes it a useful tool for differentiating between closely related species (Brown et al., 1979)—a tool that is especially important when significant variations occur between species, but not within species (Hill et al., 2001; Blair et al., 2006; Chow et al., 2006a).

Age, growth, and reproduction of dolphinfish (Coryphaena hippurus) caught off the coast of North Carolina

Age, growth, and reproductive data were obtained from dolphinfish (Coryphaena hippurus, size range: 89 to 1451 mm fork length [FL]) collected between May 2002 and May 2004 off North Carolina. Annual increments from scales (n=541) and daily increments from sagittal otoliths (n=107) were examined; estimated von Bertalanffy parameters were L∞ (asymptotic length)=1299 mm FL and k (growth coefficient)=1.08/yr. Daily growth increments reduced much of the residual error in length-at-age estimates for age-0 dolphinfish; the estimated average growth rate was 3.78 mm/day during the first six months. Size at 50% maturity was slightly smaller for female (460 mm FL) than male (475 mm FL) dolphinfish. Based on monthly length-adjusted gonad weights, peak spawning occurs from April through July off North Carolina; back-calculated hatching dates from age-0 dolphinfish and prior reproductive studies on the east coast of Florida indicate that dolphinfish spawning occurs year round off the U.S. east coast and highest levels range from January through June. No major changes in length-at-age or size-at-maturity have occurred since the early 1960s, even after substantial increases in fishery landings.

Importance of shoreface sand ridges as habitat for fishes off the northeast coast of the United States

To determine if shoreface sand ridges provide unique habitats for fish on the inner continental shelf, two cross-shelf trawl surveys (23 km in length) were conducted in southern New Jersey (July and September 1991−95 with a beam trawl and July and September 1997−06 with an otter trawl) to assess whether species abundance, richness, and assemblages differed on and away from the ridge. The dominant species collected with both gears were from the families Paralichthyidae, Triglidae, Gobiidae, Serranidae, Engraulidae, Stromateidae, and Sciaenidae. Overall abundance (n=41,451 individuals) and species richness (n=61 species) were distributed bimodally across the nearshore to offshore transect, and the highest values were found on either side of the sand ridge regardless of gear type. Canonical correspondence analysis revealed three species assemblages: inshore (<5 meters depth), near-ridge (9−14 meters depth), and offshore (>14 meters depth), and variation in species composition between gear types. Environmental factors that corresponded with the assemblage changes included depth, temperature, distance from the top of the ridge, and habitat complexity. The most abundant near-ridge assemblages were distinct and included economically important species. Sand ridges of the inner continental shelf appear to be important habitat for a number of fish species and therefore may not be a suitable area for sand and gravel mining.

Diel variation in vertical distribution of an offshore ichthyoplankton community off the Oregon coast

We examined the diel ver-tical distribution, concentration, and community structure of ichthyoplank-ton from a single station 69 km off the central Oregon coast in the northeast Pacific Ocean. The 74 depth-stratified samples yielded 1571 fish larvae from 20 taxa, representing 11 families, and 128 fish eggs from 11 taxa within nine families. Dominant larval taxa were Sebastes spp. (rockfishes), Stenobra-chius leucopsarus (northern lampfish), Tarletonbeania crenularis (blue lan-ternfish), and Lyopsetta exilis (slender sole), and the dominant egg taxa were Sardinops sagax (Pacific sardine), Icichthys lockingtoni (medusafish), and Chauliodus macouni (Pacific viperfish). Larval concentrations generally increased from the surface to 50 m, then decreased with depth. Larval concentrations were higher at night than during the day, and there was evidence of larval diel vertical migration. Depth stratum was the most important factor explaining variability in larval and egg concentrations.