Shortspine Thornyhead Research Articles

Effects of capture on acute and long-term reflex impairment, survival, and health of a deepwater fish: Shortspine thornyhead (Sebastolobus alaskanus).

Shortspine thornyhead (Sebastolobus alaskanus) are a benthic, deepwater species in the family Scorpaenidae. They have been tagged annually in Alaska since 1992, but have a low tag return rate of 1.6%. This may be at least partially attributed to post-release mortality related to capture. In this study, 21 shortspine thornyhead were caught on bottom hook-and-line longline gear and immediately given reflex tests. Eighteen were transported to the laboratory and held for 10–42 days, given reflex tests again, and then given postmortem examinations, including histopathology of tissues; three were given postmortem examinations after reflex tests on the vessel. There were no histological findings that could be directly linked to capture and holding; however, there were occurrences of myxozoan (protozoa) and metazoan (nematode) parasites, sometimes associated with minor inflammation. The vibration response reflex was found in only 24% of fish on deck and in 56% of fish after holding in the laboratory. The vestibular-ocular response was present in 47% of fish on deck and 89% of fish in the laboratory. A fish’s ability to right itself was successful on deck in 43% of fish (an additional 19% responded slowly) and 100% in the laboratory. Some reflex impairments may be permanent or may take more than days or weeks to improve. Reflex responses to other tests, the tail grab, gag, and operculum flare, were 95–100% successful on deck and later in the laboratory. A lack of reflexes may increase the risk of predation after release and may affect other behaviors related to survival and productivity.

Otolith chemistry indicates age and region of settlement of immature shortspine thornyhead Sebastolobus alascanus in the eastern Pacific Ocean

Shortspine thornyhead Sebastolobus alascanus are widely distributed along the eastern Pacific coast and are assessed as a demographically homogeneous stock off the coasts of California, Oregon and Washington. The validity of this assumption has been questioned because data suggest complex ontogenetic movements. Otolith microchemistry applied to immature fish was used to determine the age of settlement and the population structure of S. alascanus. Samples were collected from 2011-2013 from bottom trawl surveys in 5 areas along the coasts of (1) Washington, (2) northern Oregon, (3) southern Oregon and northern California, (4) central California and (5) southern California. The Ba:Ca ratio, measured from the primordium to the margin of otoliths, corresponds to the pelagic and benthic phases of immature fish. This ratio decreased steadily before the formation of the first annulus and increased thereafter. Water masses along the bathymetric gradient mostly correlated with the distribution of otolith trace element (Mg:Ca, Ba:Ca) and stable isotope (δ18O and δ13C) ratios on the continental shelf. These results indicate that the population of immature fish belongs to 2 distinct groups, distributed north and south of Cape Mendocino. Accordingly, the performance of a k-nearest-neighbor classifier was highest when structured based on these 2 regions, with 94 and 69% cross-validated classification accuracy, respectively into the northern and southern groups. These results confirm that S. alascanus settle after nearly 1 yr of pelagic life and show that otolith chemistry can be used to test critical hypotheses regarding the migration and population structure of this species.

Effects of changing ocean temperatures on ecological connectivity among marine protected areas in northern British Columbia

Marine protected areas (MPAs) are important conservation tools for safeguarding marine systems, yet they are increasingly impacted by climate change. Connectivity is a fundamental aspect of MPA design and evaluation, but regional patterns of marine ecological connectivity are often not well understood, nor how connectivity patterns may be affected by climate change. Our objective was to assess how ecological connectivity between MPAs may shift with projected ocean temperature changes in the Northern Shelf Bioregion in British Columbia, Canada, and demonstrate a potential approach that can be used in other systems. We conducted a case study with Dungeness Crab (Metacarcinus magister) and Shortspine Thornyhead (Sebastolobus alascanus) using benthic temperature outputs from a regional ocean model for hindcast (1981–2010) and future (2041–2070) periods coupled with species’ environmental preference information. We evaluated MPA exposure to projected temperature changes and suitability for the adult stage of the focal species. Using existing least-cost and circuit theory-based tools more often applied in terrestrial systems, we identified potential linkages between MPAs via adult movement, simulating both optimal and probabilistic paths, then compared MPA interconnectedness between time periods. There was a marked decrease in MPA suitability and interconnectedness for Shortspine Thornyhead under projected future climates, while there was a marked increase in MPA suitability for Dungeness Crab and minor increase in MPA interconnectedness. Given the contrasting results in connectivity changes when examining just two species, this study highlights the challenge of building climate resilience in MPA network designs with multispecies objectives.

Spatio-temporal patterns in juvenile habitat for 13 groundfishes in the California Current Ecosystem.

Identifying juvenile habitats is critical for understanding a species’ ecology and for focusing spatial fishery management by defining references like essential fish habitat (EFH). Here, we used vector autoregressive spatio-temporal models (VAST) to delineate spatial and temporal patterns in juvenile density for 13 commercially important species of groundfishes off the US west coast. In particular, we identified hotspots with high juvenile density. Three qualitative patterns of distribution and abundance emerged. First, Dover sole Microstomus pacificus, Pacific grenadier Coryphaenoides acrolepis, shortspine thornyhead Sebastolobus alascanus, and splitnose rockfish Sebastes diploproa had distinct, spatially-limited hotspots that were spatially consistent through time. Next, Pacific hake Merluccius productus and darkblotched rockfish Sebastes crameri had distinct, spatially limited hotspots, but the location of these hotspots varied through time. Finally, arrowtooth flounder Atheresthes stomias, English sole Parophrys vetulus, sablefish Anoplopoma fimbria, Pacific grenadier Coryphaenoides acrolepis, lingcod Ophiodon elongatus, longspine thornyhead Sebastolobus altivelis, petrale sole Eopsetta jordani, and Pacific sanddab Citharichthys sordidus had large hotspots that spanned a broad latitudinal range. These habitats represent potential, if not likely, nursery areas, the location of which will inform spatial management.

Age validation of four rockfishes (genera Sebastes and Sebastolobus) with bomb-produced radiocarbon

In rockfish (Family Scorpaenidae), age determination is difficult and the annual nature of otolith growth zones must be validated independently. We applied routine age determination to four species of Gulf of Alaska rockfish: two shallower-water species, namely harlequin rockfish (Sebastes variegatus) and redstripe rockfish (Sebastes proriger), and two deep-water species, namely shortspine thornyhead (Sebastolobus alascanus) and shortraker rockfish (Sebastes borealis). The estimated ages (counts of presumed annual growth zones in the otoliths) were then evaluated with bomb-produced radiocarbon (14C) and Bayesian modelling with Markov chain Monte Carlo simulations. This study successfully demonstrated the level of accuracy in estimated ages of redstripe rockfish (a 35% probability of underageing, and ~5% probability of overageing) and harlequin rockfish (a 100% probability that they were underaged by ~3 or 4 years). Measured Δ14C in shortspine thornyhead and shortraker rockfish otoliths was lower and increased later than expected. Hence, incorrect age determination could not be evaluated. This is likely caused by dissimilar environmental and biological availability of 14C between these two species and the Pacific halibut (Hippoglossus stenolepis) reference chronology, or underageing of these two species.

First results of the tagging of shortspine thornyhead, Sebastolobus alascanus, in Alaska

Shortspine thornyhead (Sebastolobus alascanus) is a commercially valuable deep dwelling rockfish species that has been tagged in Alaska waters since 1992. These tagging results are the primary analyses available for evaluating the movement of this species, which will allow managers to determine the appropriate geographic scale of management. A total of 13,897 tagged fish have been released, with 228 recoveries reported during 1992–2016. Of the returned tags, 19% traveled <2M (nm) between tagging and recovery location, 36% traveled 2–5nm, 18% traveled 6–10nm, 12% traveled 11–50nm, 4% traveled 51–100nm, and 11% traveled >100nm. While a small percentage of tagged shortspine thornyhead traveled large distances, at times crossing management and international boundaries, the low movement rate indicates that the current scale of management for shortspine thornyhead rockfish in Alaska appears to be appropriate.

Improving Catch Utilization in the U.S. West Coast Groundfish Bottom Trawl Fishery: an Evaluation of T90‐Mesh and Diamond‐Mesh Cod Ends

AbstractThe limited‐entry bottom trawl fishery for groundfish along the U.S. West Coast operates under a catch share program, which is implemented with the intention of improving the economic efficiency of the fishery, maximizing fishing opportunities, and minimizing bycatch. However, stocks with low harvest guidelines have limited the ability of fishermen to maximize their catch of more abundant stocks. Size‐selection characteristics of 114‐mm and 140‐mm T90‐mesh cod ends and the traditional 114‐mm diamond‐mesh cod end were examined by using the covered cod end method. Selection curves and mean L50 values (length at which fish had a 50% probability of being retained) were estimated for two flatfish species (Rex Sole Glyptocephalus zachirus and Dover Sole Microstomus pacificus) and two roundfish species (Shortspine Thornyhead Sebastolobus alascanus and Sablefish Anoplopoma fimbria). Mean L50 values were smaller for flatfishes but larger for roundfishes in the 114‐mm T90 cod end compared to the diamond‐mesh cod end. For Rex Sole, Dover Sole, and Shortspine Thornyheads, selectivities of the 140‐mm T90 cod end were significantly different from those of the other cod ends; the 140‐mm T90 cod end was most effective at reducing the catch of smaller‐sized fishes but with a considerable loss of larger‐sized marketable fishes. Findings suggest that T90 cod ends have potential to improve catch utilization in this multispecies fishery.

Killer whale (Orcinus orca) depredation effects on catch rates of six groundfish species: implications for commercial longline fisheries in Alaska

AbstractPeterson, M. J., Mueter, F., Hanselman, D., Lunsford, C., Matkin, C., and Fearnbach, H. 2013. Killer whale (Orcinus orca) depredation effects on catch rates of six groundfish species: implications for commercial longline fisheries in Alaska. – ICES Journal of Marine Science, 70: 1220–1232. Killer whale (Orcinus orca) depredation occurs when whales damage or remove fish caught on longline gear. This study uses National Marine Fisheries Service longline survey data from 1998–2011 to explore spatial and temporal trends in killer whale depredation and to quantify the effect of killer whale depredation on catches of six groundfish species within three management areas in Alaska: the Bering Sea, Aleutian Islands and Western Gulf of Alaska. When killer whales were present during survey gear retrieval, whales removed an estimated 54–72% of sablefish (Anoplopoma fimbria), 41–84% of arrowtooth flounder (Atheresthes stomias) and 73% (Bering Sea only) of Greenland turbot (Reinhardtius hippoglossoides). Effects on Pacific halibut (Hippoglossus stenolepis) and Pacific cod (Gadus macrocephalus) were significant in the Western Gulf only with 51% and 46% reductions, respectively. Overall catches (depredated and non-depredated sets) for all groundfish species significantly impacted by killer whale depredation were lower by 9–28% (p &lt; 0.05). Effects on shortspine thornyhead (Sebastolobus alascanus) catches were not significant in any management area (p &gt; 0.05). These results provide insight into the potential impacts of killer whale depredation on fish stock abundance indices and commercially important fisheries in Alaska and will inform future research on apex predator–fisheries interactions.

An Abnormally Colored Redbanded Rockfish, Sebastes babcocki

Four species of eastern North Pacific rockfishes of the genus Sebastes are easily distinguished from their congeners by the coloration characteristic of broad lateral banding. These species are the Tiger Rockfish, S. nigrocinctus; Treefish, S. serriceps; Flag Rockfish, S. rubrivinctus; and Redbanded Rockfish, S. babcocki. These species are shown to be closely related and have been placed in the Sebastichthys clade by Hyde and Vetter (2007). The Tiger Rockfish and Treefish are distinguished by differences in their general body form and coloration of the banding pattern. The Treefish invariably exhibits alternating black, brown, or dark green and yellow bars, and the lips are distinctly pink to red (rarely without coloration). The Tiger Rockfish manifests greater variation in banding with the darker bars being primarily red, but can vary from reddish-black to reddish-brown. The alternating lighter bars are mainly white, but occasionally show a reddish hue. The Flag and Redbanded rockfishes possess alternating red and white bars (Love et al., 2002). The general similarity in body shape and color pattern between the latter two species was cause for them to be considered conspecific from shortly after the year of description of S. babcocki (Thompson, 1915) until Rosenblatt and Chen (1972) clarified the distinction of these species and pointed out a number of meristic and morphological characteristics that definitively separate these two species. The Flag Rockfish was described in the late 1800’s (Jordan and Gilbert, 1880). On 10 February 2004, a uniformly red rockfish (Fig. 1) was encountered by Diane Haas, then a Fishery Technician with the Pacific States Marine Fisheries Commission, during routine sampling of commercial groundfishes. The F/V Alex Kevin D had unloaded three market categories of groundfishes: Longspine Thornyhead, Sebastolobus altivelis; Shortspine Thornyhead, S. alascanus; and Blackgill Rockfish, Sebastes melanostomus, which were to be sampled. The uniformly red rockfish was included in the Blackgill Rockfish market category, where a 50 pound cluster was randomly selected from a total landing of 764 pounds. The species composition of the cluster consisted of Blackgill Rockfish, one Rosethorn Rockfish, S. helvomaculatus, and the uniformly red rockfish. Also present in the landing, but not included in the sample, were at least two Rougheye Rockfish, S. aleutianus, (from California the species is now considered as Blackspotted Rockfish, Sebastes melanostictus [Orr and Hawkins, 2008]). The fishes were taken in Monterey Bay (ca. 36u479 N, 122u079 W) by commercial longline gear on the continental slope at a depth of 200–260 fathoms (366–475 meters). The red rockfish was not immediately identifiable with any of the red-colored, outer shelf-upper slope rockfishes normally encountered off central California and was Bull. Southern California Acad. Sci. 111(1), 2012, pp. 22–24 E Southern California Academy of Sciences, 2012

Shortspine thornyhead and rockfish (Scorpaenidae) distribution in response to substratum, biogenic structures and trawling

Learmonth Bank in northern British Columbia sustains an active trawl fishery that returns large bycatches of deep-sea sponges and corals. To examine effects of biogenic structures on the distribution of fish, we examined nearly 30 km of high-definition imagery from a remotely oper- ated vehicle and documented locations of 2770 scorpaenid fish. The 2 local genera have similar abun- dances, averaging about 1.2 individuals 100 m -2 , but have different spatial abundance patterns: shortspine thornyhead Sebastolobus alascanus are randomly distributed on featureless substrata and their abundance increases with depth. Rockfish Sebastes spp. associate with higher seafloor relief nonrandomly and select for sponges and corals over the inert substrata alone; 95% of the rockfish occurred on 27% of the seafloor surveyed. Sponges (Demospongia and Hexactinellida) were abun- dant on the bedrock and boulders of the bank and adjacent moraine and covered 30 to 55% of the seafloor compared with 1% of the sediment and aggregates of the surrounding basin. The majority of rockfish (80%) occurred with sponges ≥50 cm in height, and even beds of short sponges attracted 4 times as many rockfish than did substrata with no large epifauna. While over half of primnoid corals over 30 cm tall had associated rockfish, less than 2% of the seafloor had large coral, and small coral had no associated rockfish. On the adjacent seafloor with past trawling activity, Primnoa pacifica was 13 times less abundant, and large corals and sponges were rare. Thornyhead abundance doubled but rockfish had a 3-fold reduction in numbers. Our study indicates that degradation of biogenic struc- tures is a long-term detriment to rockfish species and, although the mechanism remains unclear, our data suggest it occurs through the destruction of a habitat that is more effective for shelter than rough inert seafloor.

New data on the reproductive biology of shortspine thornyhead Sebastolobus alascanus (Sebastidae) in the northwestern Pacific

New data on fecundity, sex ratio in different size groups, and the rate of sexual maturation of shortspine thornyhead Sebastolobus alascanus in the northwestern part of the Pacific Ocean are provided. Individual absolute fecundity of the studied females varies in the range of 175 000–821000 (on average, 392500) eggs. In Pacific waters off the Kuril Islands and Kamchatka, among individuals with a length to 41 cm, males dominate; in size groups of 42–59 cm, sex ratio is almost equal; among larger fish, females prevail. In the western part of the Bering Sea among analyzed fish with a length to 44 cm, sex ratio is almost equal; among larger individuals, females dominate. Half of males and females of shortspine thornyhead off the eastern coast of the northern Kuril Islands and southeastern Kamchatka mature at a length of approximately 41 cm that can be recommended as a commercial size for the given species in this area.

Predicting presence and abundance of demersal fishes: a model application to shortspine thornyhead Sebastolobus alascanus

Predicting the abundance of marine fishes based on habitat models is often difficult due to the presence of large numbers of zero observations. The objective of this study was to analyze the ability of a 2-stage model to predict the presence and abundance of a rockfish species, shortspine thornyhead Sebastolobus alascanus. The data used for these analyses were collected during bottom- trawl surveys of the Gulf of Alaska ecosystem from 1993 to 2007 and in the Aleutian Islands ecosys- tem from 1994 to 2006. The presence of shortspine thornyhead was predicted from the 5th and 95th percentiles of the cumulative distribution function resampled over depth and temperature. The results predicted shortspine thornyhead would not occur at depths 671 m, and presence or absence was correctly predicted at 86.3% of the trawl survey stations. Environmental variables were then used to model shortspine thornyhead abundance at stations where presence was pre- dicted. The best-fitting model of abundance included the variables depth, local slope, thermocline temperature, shrimp catch per unit effort (CPUE), and an index of predation refuge. The model explained 72.4% of the variation in 1993-2005 Gulf of Alaska survey data and 73.7% of the variation in the 2007 data from the Gulf of Alaska. The model explained only 23.9% of the variation in short- spine thornyhead CPUE from the Aleutian Islands bottom-trawl surveys from 1994 to 2006. The habi- tat model included important variables for survival and growth in order to provide more biologically meaningful results than with other modeling methods.

Habitat-based submersible assessment of macro-invertebrate and groundfish assemblages at Heceta Bank, Oregon, from 1988 to 1990

Exploitation of groundfish off the U.S. Pacific coast reached maximum levels during the 1990s, resulting in severe declines in at least nine species of groundfish. From 1988 to 1990, we used the 2-man submersible Delta to make 42 dives and run replicate visual belt transects at six stations ranging from 67–360 m in depth at Heceta Bank on the outer continental shelf of Oregon. We identified four major habitats and associated benthic macroinvertebrate and groundfish assemblages: (1) shallow rock ridges and large boulders (< 100 m deep) dominated by basket stars, juvenile rockfishes, yelloweye rockfish, and lingcod; (2) mid-depth small boulder-cobbles (100–150 m) dominated by crinoids, brittle stars, rosethorn, pygmy/Puget sound, and canary rockfishes; (3) deep cobble (150–200 m) dominated by crinoids, brittle stars and various small rockfish species, and (4) deep mud slope (> 200 m) dominated by fragile urchins, sea cucumbers, shortspine thornyhead, and flatfishes. Although substantial interannual variation in groundfish abundance among seafloor types was evident in the 12 most abundant and/or commercially important fish taxa sampled, high variance resulted in statistically significant differences among years only in juvenile rockfishes. These data provide a baseline for future comparisons exploring long-term change this continental-shelf ecosystem.

Comparison of trawled vs untrawled mud seafloor assemblages of fishes and macroinvertebrates at Coquille Bank, Oregon

We report the first quantitative comparison of trawled vs untrawled mud seafloor communities off the west coast of North America. Using a manned submersible, we ran visual transects at Coquille Bank, 25 km off the central coast of Oregon, USA, including six half-hour (mean length 1184 m) transects over mud seafloors 183–361 m deep. The shallowest transects were untrawled, whereas deeper transects were heavily trawled, as evidenced by extensive trawl-door tracks. Differences between trawled and untrawled seafloor assemblages were striking. We observed 23% more fish over untrawled compared to trawled seafloors, and recorded 27 fish species on untrawled bottoms, but only 19 species on trawled seafloors. Regarding benthic invertebrates, density of individuals was 6 times greater on untrawled compared to trawled bottoms. Nonetheless, we observed 11 taxa on trawled seafloors and only 6 taxa on untrawled bottoms. Principal components analysis (PCA) defined the untrawled assemblage as characterized by sea pens, ratfish, sablefish, ronquil, slender sole, and poacher. PCA defined the trawled assemblage as characterized by seastars, hermit crabs, bigfin eelpout, Dover sole, hagfish, and shortspine thornyhead. In untrawled areas, there was no correlation between sea-pen density and total fish density, whereas in trawled areas, there was a marginally inverse correlation between the density of trawl-door tracks and total fish density. The dominant fishes and macroinvertebrates on trawled seafloors are known mobile scavengers that may aggregate along trawl-door tracks. Sea pens that dominated untrawled bottoms are sessile, slow-growing, long-lived species that are likely to recover slowly from physical disturbance. We conclude that the observed differences between trawled and untrawled communities were the result of groundfishing activities rather than local environmental differences. Given that habitat considerations for groundfish management in this region focus exclusively on rocky seafloors, it seems prudent to consider the adverse effects of bottom trawling on mud seafloor ecosystems of the continental shelf and slope.

Protecting rockfish through gear design: development of a selective flatfish trawl for the U.S. west coast bottom trawl fishery

This study evaluated the potential to reduce the bycatch of rockfish (Sebastes spp.) in a flatfish trawl fishery by developing a selective trawl that separates flatfish from rockfish using differences in their behavior as the trawl net approaches. Using an alternate haul, randomized block design, we compared catches between a commonly used combination trawl and a newly designed, low-rise trawl incorporating a "cutback" headrope. For most of the target flatfish species, the experimental trawl had a 25–59% higher catch rate (kilograms) than the control net (P &lt; 0.05), consistent with greater footrope length in the experimental trawl. Increased catches of some small rockfish, skates, and sablefish (Anoplopoma fimbria) were also observed (P &lt; 0.05). The catches of many larger roundfish and rockfish species, including canary rockfish (Sebastes pinniger), redstripe rockfish (Sebastes proriger), Pacific hake (Merluccius productus), and shortspine thornyhead (Sebastolobus alascanus) more than 25 cm long, were reduced from 34 to 97% in the experimental trawl (P &lt; 0.05). Under weak-stock management conditions, in which the bycatch of overfished rockfish species limits directed flatfish fisheries, trawl designs that permit nontarget species to escape before entrainment can significantly reduce bycatch mortality and prevent premature closures of directed flatfish fisheries.

Reproductive Biology and Ecology of Shortspine Thornyhead Rockfish, Sebastolobus alascanus, and longspine thornyhead rockfish, S. altivelis, from the northeastern Pacific Ocean

We examined the reproductive biology and estimated life history parameters for female shortspine thornyhead, Sebastolobus alascanus, and longspine thornyhead, S. altivelis, from histological samples prepared from specimens collected from both Alaska and the West Coast of the United States. Both species spawn pelagic gelatinous egg masses, although timing differs between taxa and locations. Shortspines spawn between April and July in Alaska and between December and May along the West Coast. Longspines spawn between January and April along the West Coast. Length at 50% maturity differed between species and areas, with shortspines at 21.48 cm in Alaska and 18.19 cm on the West Coast, and longspines at 17.83 cm on the West Coast. We used the gonadosomatic index to estimate instantaneous rates of natural mortality (M). Values of M differed little between species and areas despite substantial differences in temperature and dissolved oxygen concentrations. Estimates for shortspines from both Alaska and the West Coast ranged between 0.013 and 0.017, while longspines from the West Coast showed an M value of 0.015. Such low estimates of M suggest Sebastolobus are extremely long-lived.

The Longspine Thornyhead Fishery along the West Coast of Vancouver Island, British Columbia, Canada: Portrait of a Developing Fishery

Abstract A fishery for thornyhead Sebastolobus spp. started in the early 1990s along the Pacific coast of Canada, primarily in response to market demand from Japan. As the fishery evolved, the deepwater longspine thornyhead S. altivelis became a desirable species because it is easily targeted and commands high prices. Its congener, shortspine thornyhead S. alascanus, largely remained a bycatch species in other mid-depth fisheries along the continental slope. This paper describes the developing longspine thornyhead fishery off the western coast of Vancouver Island, British Columbia. We illustrate how the fishery migrated from its place of origin, possibly to maintain high catch rates as the resource was depleted. Analyses of the factors that significantly influence catch rates demonstrate that a model without factor interactions does not adequately describe the data. Length analysis shows that longspine thornyheads decrease in size with depth, a trend opposite to that for shortspine thornyheads. We also in...

Population genetics, phylogeography, and systematics of the thornyhead rockfishes (Sebastolobus) along the deep continental slopes of the North Pacific Ocean

Population genetic, phylogeographic, and systematic relationships are elucidated among the three species comprising the thornyhead rockfish genus Sebastolobus (Teleostei: Scorpaenidae). Genetic variation among sampling sites representing their extensive ranges along the deep continental slopes of the northern Pacific Ocean is compared using sequence data from the left domain of the mtDNA control region. Comparisons are made among the shortspine thornyhead (S. alascanus) (from seven locations), the longspine thornyhead (S. altivelis) (from five sites), which are sympatric in the northeast, and the broadbanded thornyhead (S. macrochir) (a single site) from the northwest. Phylogenetic trees rooted to Sebastes show that S. macrochir is the sister taxon of S. alascanus and S. altivelis. Intraspecific genetic variability is appreciable, with most individuals having unique haplotypes. Gene flow is substantial among some locations and others diverged significantly. Genetic divergences among sampling sites for S. alascanus indicate an isolation by geographic distance pattern. Genetic divergences for S. altivelis are unrelated to the hypothesis of isolation by geographic distance and appear to be more consistent with the hypothesis of larval retention in currents and gyres. Differences in geographic genetic patterns between the species are attributed to life history differences in their relative mobilities as juveniles and adults.

Population genetics, phylogeography, and systematics of the thornyhead rockfishes (&lt;i&gt;Sebastolobus&lt;/i&gt;) along the deep continental slopes of the North Pacific Ocean

Population genetic, phylogeographic, and systematic relationships are elucidated among the three species comprising the thornyhead rockfish genus Sebastolobus (Teleostei: Scorpaenidae). Genetic variation among sampling sites representing their extensive ranges along the deep continental slopes of the northern Pacific Ocean is compared using sequence data from the left domain of the mtDNA control region. Comparisons are made among the shortspine thornyhead (S. alascanus) (from seven locations), the longspine thornyhead (S. altivelis) (from five sites), which are sympatric in the northeast, and the broadbanded thornyhead (S. macrochir) (a single site) from the northwest. Phylogenetic trees rooted to Sebastes show that S. macrochir is the sister taxon of S. alascanus and S. altivelis. Intraspecific genetic variability is appreciable, with most individuals having unique haplotypes. Gene flow is substantial among some locations and others diverged significantly. Genetic divergences among sampling sites for S. alascanus indicate an isolation by geographic distance pattern. Genetic divergences for S. altivelis are unrelated to the hypothesis of isolation by geographic distance and appear to be more consistent with the hypothesis of larval retention in currents and gyres. Differences in geographic genetic patterns between the species are attributed to life history differences in their relative mobilities as juveniles and adults.

Cod-end mesh size selection for rockfish and flatfish of the US West Coast

Size selection characteristics of five cod-ends (114-mm, 127-mm and 140-mm diamond, and 114-mm and 127-mm square meshes) were tested through alternate-haul experiments performed under commercial fishing conditions in 1988–1990, with a 76-mm diamond mesh cod-end as standard. Overall selectivity curves for five flatfish species (arrowtooth flounder, Atheresthes stomias, and Dover, Microstomus pacificus, english, Parophrys vetulus, rex, Glyptocephalus zachirus, and petrale sole, Eopsetta jordanii) and five rockfish species (shortspine thornyhead, Sebastolobus alascanus, Pacific Ocean perch, Sebastes alutus, and widow, S. entomelas, yellowtail, S. flavidus, and canary rockfish, S. pinniger) were estimated using the Share Each Length Catch Total (SELECT) method and four types of selection ogives (logistic, probit, negative extreme value and Gompertz) on weighted pooled length distributions. The negative extreme value curve provided the best fits to more than half of the data, implying asymmetry in the retention of small and very large fish. Lengths of 50% retention increased with increasing mesh sizes for both the diamond and square mesh cod-ends, with rockfish providing on average larger values than flatfish. In general, the 114-mm square mesh cod-end retained more small fish than the other cod-ends. Thus, compared to the currently used 114-mm diamond mesh, it is not a good alternative to reduce discard or retention of immature fish. On the other hand, the 127-mm square and diamond, and 140-mm diamond mesh cod-ends reduced the retention of immature fish for many of the species. Thus, these cod-ends seem acceptable for biologically conservative management regulations.