Pacific Halibut Research Articles

Pacific halibut chronology of bomb radiocarbon in otoliths from 1944 to 1981 and a validation of ageing methods

Pacific halibut Hippoglossus stenolepis of known age were used to create a reference chronology of radiocarbon levels for the years 1944–1981. Levels of radiocarbon in Pacific halibut otoliths pre‐1958 were among the lowest reported to date, but radiocarbon levels increased dramatically post‐1960. Subsequently, this reference chronology was used to validate ages determined using the standard break and burn and surface ageing technique. These older fish were collected at a later date but were born during this period of rapidly increasing radiocarbon levels. Otolith cores were compared to the reference chronology based upon the presumed birth year determined from annulus counts and year of capture. The ages derived from both break and burn and surface ageing methods were determined to be accurate.

A Conditional Constant Catch Policy for Managing the Pacific Halibut Fishery

Abstract Since 1985, the staff of the International Pacific Halibut Commission (IPHC) has used a constant harvest rate policy—currently 20% of exploitable biomass—to estimate the yield currently available from Pacific halibut Hippoglossus stenolepis stock. This paper outlines a more stable alternative policy in which yield is held constant at some ceiling level so long as taking that yield would not result in a total exploitation rate exceeding a specified ceiling rate. During any periods of low abundance, the policy would revert to a constant harvest rate policy at the ceiling rate. The ceiling harvest rate would be chosen so as to assure that spawning biomass remained above a specified minimum. A policy of this kind could produce a yield similar to the present 20% constant harvest rate policy but with much less year-to-year variation attributable to changes in stock abundance, assessment methods, and estimated removals by other fisheries.

Behavioral mechanisms underlying the refuge value of benthic habitat structure for two flatfishes with differing anti-predator strategies

Juvenile flatfish habitat is usually modeled on the basis of sediment grain-size, depth and temperature. Recent evidence indicates that some juvenile flatfishes associate with emergent structures such as sponge, shell and other biogenic and bed-form features of otherwise low-relief shelf habitats. In laboratory experiments we examined the habitat preference and effects of habitat structure upon predation vulnerability of sub-yearling (Age-0) Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra. When given the choice between bare sand or sand with 16% sponge coverage, halibut demonstrated strong preference for sponge, while rock sole showed no preference. Larger Age-2 halibut (used as predators in the subsequent experi- ment) also preferred sponge, but this preference declined with increasing hunger. When allowed to forage for Age-0 flatfishes in either bare sand or sponge, predators consumed more prey in sand and consumed more Age-0 halibut than rock sole. We were able to determine which behavioral processes in the predator-prey interaction were modified by the presence of habitat structure. Predator-prey encounter rates decreased in the sponge habitat as predator search was impeded: predators paused more frequently and swam more slowly to maneuver through the sponges. Sponges also tended to hinder the pursuit of prey. Rock sole utilized stereotypic flatfish defense-mechanisms, relying upon immobility, burial and crypsis, and were less likely to flush at a predator's approach than halibut. Halibut have a less developed ability to mimic sediments, but a deeper/narrower body that confers greater swimming speed, and were more likely to flush as a predator approached. Once they had flushed and were pursued by a predator, halibut were more likely to escape than were rock sole. These experiments support an accumulating body of evidence that emergent structure, in otherwise low-relief benthic habitats, may play an important role in the ecology of some juvenile flatfishes. Removal of emergent structure by towed fishing gear and other anthropogenic and/or natural distur- bance may influence patterns of distribution for juvenile halibut, as fish redistribute to less preferred habitat, and may decrease survival rates through increased losses to predation.

A MODEL FOR THE WORLD: 80 YEARS OF MODEL DEVELOPMENT AND APPLICATION AT THE INTERNATIONAL PACIFIC HALIBUT COMMISSION

ABSTRACT. This is a short history of modeling work done by the staff of the International Pacific Halibut Commission, from the pioneering work of Thompson and Bell through the present.

Active and Passive Management of the Recreational Fishery for Pacific Halibut off the U.S. West Coast

Abstract Since the 1970s, the recreational fishery for Pacific halibut Hippoglossus stenolepis off the West Coast of the United States (Washington, Oregon, and California) has grown substantially, thereby reducing the amount of halibut available to other users. A catch sharing plan (CSP) was developed in 1988 to allocate the available yield among recreational fishers, commercial fishers, and treaty Indian tribes. The CSP defines the share of the total available catch allocated to each group and further subdivisions within the groups. The most complex allocation is that for the recreational fishery, which is managed by the agencies of the three coastal states, the federal fisheries agency, and an international commission that has overall responsibility for the preservation of the species. Management tools for the recreational fishery include seasons, bag limits, closed areas, vessel licensing and registration, minimum length limits, and various levels of catch monitoring. Although the recreational fishery ...

Biomarkers in fish from Prince William Sound and the Gulf of Alaska: 1999-2000.

To test the hypothesis that biomarker levels in fish collected at Prince William Sound (PWS) sites impacted by the 1989 Exxon Valdez oil spill were higher than those collected at unimpacted sites, a 1999-2000 study collected five fish species and associated benthic sediments from 21 sites in PWS and the eastern Gulf of Alaska (GOA). PWS sites were divided in three oiling categories based upon 1989 shoreline assessments: nonspill path (NSP), spill path oiled (SPO), and spill path not oiled (SPNO). Rockfish (N = 177), rock sole (N = 30), and kelp greenling (N = 49) were collected at near-shore locations (approximately 50-500 m from shore); Pacific halibut (N = 131) and Pacific cod (N = 81) were collected further offshore (approximately 500-7000 m). Fish were assayed for bile fluorescent aromatic contaminants (FAC) and cytochrome P4501A (CYP1A) levels measured as liver ethoxyresorufin O-deethylase (EROD) activity and by immunohistochemistry (IHC) of various tissues. For all species studied at all sites, bile FAC concentrations and CYP1A levels were low and in the same range for fish collected at PWS SPO and SPNO sites relative to NSP sites in PWS and the GOA. Consequently, the hypothesis is rejected for the species studied. The bile FAC results further indicate a pervasive exposure of fish at all sites, including those in the GOA far removed from the effects of the spill, to low levels of polycyclic aromatic hydrocarbons. Analysis of the benthic sediments indicates that the probable sources of this exposure are petrogenic hydrocarbons derived from natural oil seeps and eroding sedimentary rocks in the eastern GOA.

Stable isotopic composition of otoliths from tagged Pacific halibut, Hippoglossus stenolepis

Data from tagging studies and stable isotope ratio analyses (δ18O and δ13C) in otoliths of tagged Pacific halibut, Hippoglossus stenolepis, provided unique information about halibut distribution and area migration. The δ18O values of otoliths of individual halibut tagged in the Bering Sea and the Gulf of Alaska ranged from −0.5‰ to +1.0‰ VPDB (Vienna Peedee belemnite) in the first few years, but gradually increased to 2.0–2.5‰ VPDB when these tagged fish were recaptured as adults in waters off British Columbia. Similar isotopic variations were found in δ13C. Comparison of isotopic composition from the age-1 halibut (i.e., aragonite samples taken from the first annulus of otoliths) and the adult (ages ≥8) indicated that the ocean conditions between the Bering Sea and the northeast Pacific were markedly different over the tagging period, but the area boundaries between the Gulf of Alaska and British Columbia were not clear. We concluded that stable isotopic records in otoliths of tagged Pacific halibut were informative and particularly useful for details of subsequent movement of halibut between release and recovery.

Hunger and light level alter response to bait by Pacific halibut: laboratory analysis of detection, location and attack

Laboratory experiments with Pacific halibut Hippoglossus stenolepis revealed that hunger level had a significant effect on the first detection of bait, the number of baits located and attacked, the time required to locate and attack baits and handling times. In all cases, feeding motivation and efficiency increased with hunger. Light level influenced general locomotory activity and location and attacks on baits, but not detection or handling times. The effect of light was interactive with fish hunger level. Hungry fish could locate and consume baits in all light levels, ranging from daylight conditions to near darkness (10−8 µmoles photons m−2 s−1), but location, attack and handling times were all significantly elevated in low light conditions, and attack rates were significantly reduced. In the dark, only 50% of the baits were located and only 17% were attacked. Performance metrics were relatively similar among three higher light treatments (10−5, 10−3 and 10−1 µmoles photons m−2 s−1) where bait location and attack were more efficient. Active space and effective area associated with baited fishing gear will vary because hunger and light levels affect variation in bait detection, locomotion and feeding behaviour. Consequently, fishing activity and stock assessments that depend upon bait may be compromised by spatial and temporal variation in prey abundance, time of day, season, depth and other environmental variables that influence feeding motivation and efficiency.

Biological structures and bottom type influence habitat choices made by Alaska flatfishes

Habitats of flatfishes are ordinarily characterized on the basis of depth, sediment type, and temperature. However, features of the benthic environment such as structures created by sessile organisms and different bedforms may also influence habitat suitability. In this investigation, we tested the hypothesis that habitat choices made by juveniles of two economically important flatfishes, Pacific halibut ( Hippoglossus stenolepis Schmidt) and northern rock sole ( Lepidopsetta polyxystra Orr and Matarese), are influenced by structures on the sea floor. In the laboratory, age-0 individuals of both species demonstrated high positive selectivity for habitats with structure (natural sponges, bryozoan mimics, bivalve shells, and sand waves) over smooth sand substratum. The degree of choice was influenced significantly by density of structures, particularly sponges. Small halibut (48–77 and 90–144 mm) were more selective than larger juveniles (270–337 mm), and in sponge habitat juvenile halibut were more selective than comparably sized rock sole. Preference for habitat with structure increased significantly with increasing light level, suggesting that choices were made partially on the basis of visual cues or as related to perceived threat. However, the preference for structured habitat was maintained in darkness. Beam trawl collections made in a flatfish nursery ground near Kodiak, Alaska, revealed that the abundances of age-0 Pacific halibut and rock sole were closely correlated with amounts of shell and echinoderm bycatch in the tows, corroborating the laboratory observations of affinity for habitat structure. Strong preferences for structured habitat in young halibut and rock sole indicate the importance of benthic structures that are frequently removed by fishing gear.

The Economics of Marine Resources and Conservation Policy The Pacific Halibut Case Study with Commentary

PART I of this two-part volume is a reprint of Crutchfield and Zellner's pioneering work on the economic theory of regulation in marine resources (with special reference to the Pacific Halibut fishery), first published in 1962 by the U.S. Department of the Interior. The original publication quickly went out of print and, although some individual analyses from the study were published in academic journals, the volume in its entirety was not reprinted, and thus has been unavailable to most people. The reprint of the original study is followed in Part 2 with a commentary, where leading contemporary resource and environmental economists comment on the original study's relation to general developments in the field since. Commentaries are made by David Zilberman (University of California, Berkeley), Anthony Scott (University of British Columbia), James E. Wilen (University of California, Davis) and Frances R. Homans (University of Minnesota). The volume concludes with a recent history of the International Pacific Halibut Conservation Program by Donald McCaughran, which includes the current impact of conservation measures and policy recommendations originally made by Crutchfield and Zellner.

North Pacific Halibut and Sablefish IFQ Policy Design: Quantifying the Impacts on Processors

This study examines how the two largest individual transferable fishing quota (IFQ) policies in the United States impacted halibut and sablefish processors. A survey of processors was conducted to estimate the change in processing sector welfare, measured as the change in quasi rents before and after IFQs. The policy was efficient and harvesters were left much better off. However, most processors did not participate in the rationalization benefits and, on average, were left worse off. Expanding the survey results to the pre-IFQ population, it is estimated that the halibut processing sector lost 56% of its prior quasi rents, while sablefish processors lost 76%. Eighty-two percent of the pre-IFQ halibut processors and 96% of the sablefish processors were estimated to be absolutely worse off.

Sex-biased dispersal in a salmonid fish.

We tested the hypothesis that dispersal is sex biased in an unexploited population of brook trout, Salvelinus fontinalis, on Cape Race, Newfoundland, Canada. Based on the assumptions that trout are promiscuous and that reproductive success is limited primarily by either number of mates (males) or fecundity (females), we predicted that males would disperse greater distances than females. We also tested the hypothesis that trout populations comprise stationary and mobile individuals, predicting that males have greater mobility than females. Based on a mark-recapture study of 943 individually tagged fishes, 191 of which were recaptured over 5 years, we find strong support for our hypothesis of male-biased dispersal in brook trout. Averaged among all 11 resampling periods, males dispersed 2.5 times as far as females; during the spawning period only, male dispersal exceeded that by females almost fourfold. Both sexes were heterogeneous with respect to movement, with a lower incidence of mobility among females (29.6%) than males (41.1%); mobile males dispersed six times further than mobile females. We conclude that this sex bias reduces mate competition among male kin and decreases the probability that males will reproduce with related females.

Relationships between size-specific sediment preferences and burial capabilities in juveniles of two Alaska flatfishes

Laboratory experiments with juvenile Pacific halibut ( Hippoglossus stenolepis Schmidt) (31–150 mm TL) and northern rock sole ( Lepidopsetta polyxystra Orr and Matarese) (15–150 mm TL) were conducted to examine relationships between sediment preference, burial performance, and general morphological characteristics. Both species demonstrated significant size-dependent changes in sediment choices during the first year of life. Highest sediment selectivity occurred in the smallest individuals of both species. There was a strong positive relationship between sediment choice and ability to bury quickly and completely, although the choices made by rock sole were less specific than those of comparably sized halibut and were less closely concordant with burial capability. In both species, fish >80 mm TL were relatively nonselective, except that they avoided sediments with the largest grain size (i.e., granules and pebbles). Pacific halibut have narrower, more powerful bodies than rock sole and were stronger burrowers than rock sole. Rock sole were more cryptic than halibut in general locomotion and color-matching capability, and appear to depend to a lesser extent on burial for survival than do halibut. Association with sediment is the first line of defense for juvenile flatfishes, and the relationships shift rapidly with fish size during the first year of benthic life. Therefore, habitat descriptions and models for young post-settlement flatfishes need to be made for narrow size classes.

The effect of trawl speed on the footrope capture efficiency of a survey trawl

The effect of speed through water on the footrope capture efficiency of a survey bottom trawl was experimentally investigated by repetitively towing at three vessel speeds (2.5, 3.0 and 3.5 knots) with an auxiliary net attached underneath the trawl footrope to capture fish escaping beneath the trawl. Length-dependent capture efficiencies were then computed from the number of fish caught in both the trawl and auxiliary net. Capture efficiencies for Pacific cod Gadus macrocephalus, walleye pollock Theragra chalcogramma and Pacific halibut Hippoglossus stenolepis were not affected by fish length or trawl speed. Capture efficiency for skates Bathyraja spp. decreased with increasing trawl speed but was not affected by fish length. Capture efficiencies for arrowtooth flounder Atheresthes stomias and flathead sole Hippoglossoides elassodon increased with fish length and decreased with increasing trawl speed. Our results indicate that in areas of variable current, variation in survey catch per unit effort could be reduced for some species by standardizing towing speed to speed through water or by reducing footrope lift by the addition of sufficient weight to the trawl footrope.

Stable isotope variations in otoliths of Pacific halibut ( Hippoglossus stenolepis) and indications of the possible 1990 regime shift

Stable oxygen and carbon isotope ratios ( δ 18 O and δ 13 C ) from archived otoliths of Pacific halibut, Hippoglossus stenolepis, were measured to examine the most recent regime shifts in British Columbia and the Gulf of Alaska. δ 18 O values of these otoliths ranged from −1.5 to +2.8‰ VPDB, and were consistent with the life stages and migration behavior of halibut. δ 13 C varied from −3.3 to +0.9‰ VPDB, but did not show a transition from the juvenile to the adult stage as does δ 18 O . Evaluation of δ 18 O and δ 13 C values of mature halibut (ages 8–12) indicated that the 1977 regime shift might have a warming impact on the northeast Pacific fish stocks. In contrast, a possible regime shift around 1990 with a bottom seawater temperature decrease of about 2 °C might have occurred in both the areas. The connection between stable isotope variations in otoliths and the climate regime shifts is thus potentially useful in studying the population dynamics of Pacific halibut, and decadal scale (e.g., the last 20–30 years) ocean environmental changes.

Sediment preferences and size‐specific distribution of young‐of‐the‐year Pacific halibut in an Alaska nursery

A combination of laboratory experiments and field surveys was used to test the hypotheses that responses to sediments change with fish size and that sediment grain‐size is the predominant environmental factor affecting small‐scale distribution in young‐of‐the‐year (yoy) Pacific halibut Hippoglossus stenolepis. Laboratory tests showed that the smallest fish (31–40 mm LT) chose fine sediments (muddy and fine sands), fish 51–70 mm had high selectivity (primarily medium sand), and the largest fish (80–150 mm) were not selective although they avoided the largest grain‐sizes (pebbles and granules). Sediment preferences were correlated with size‐dependent burial capabilities. Beam trawl collections were made over a 6 year period in Kachemak Bay, Alaska, to examine the distribution of yoy Pacific halibut (14–120 mm LT) using small size classes (e.g. 10 mm intervals). Canonical correlation analysis showed that the per cent of sand in the sediment was a highly significant variable for all but one size and date combination. Catch per unit of effort (CPUE) for newly settled fish (<30 mm LT) was highest on very fine sand, fish 41–80 mm were most abundant on fine sand, and the largest yoy fish (81–120 mm) were abundant over a range of sediments from fine sand to mud. Except for the smallest fish, Pacific halibut in the field were associated with sediments somewhat finer than predicted from the laboratory experiments; however, virtually all were captured where they could bury easily. The ability of flatfish to bury and shelter in sediment is related to fish size; consequently, habitat associations shift rapidly during the first year of life. Habitat models for yoy flatfishes should consider size‐dependent shifts in capabilities and preferences.

Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nursery

Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nursery

Effects of Climate and Stock Size on Recruitment and Growth of Pacific Halibut

Abstract This paper compares long-term changes in the recruitment and growth of Pacific halibut Hippoglossus stenolepis with long-term changes in climate and stock size. It appears that environmental variability—both interdecadal and interannual—is responsible for most of the observed variation in Pacific halibut recruitment. The large changes in growth rates that occurred during the 20th century appear to have been density-dependent responses to changes in stock size, with virtually no environmental influence.

Linking sportfishing trip attributes, participation decisions, and regional economic impacts in Lower and Central Cook Inlet, Alaska

Forecasts of the regional economic impacts of changes in the demand for recreation occasioned by regulatory changes, changes in the quality of the recreation experience, or changes in average trip costs require a model that links changes in these trip attributes to individual participation decisions and population participation rates. The probability that an individual will take a particular recreational trip is described using a nonlinear random effects probit model based on variable trip attributes and individual economic and demographic characteristics. These conditional individual probabilities are transformed into predictions of changes in total recreation demand using a simulation-based sample enumeration method. The regional impacts associated with ensuing changes in primary and secondary expenditure patterns are elucidated with a stand-alone recreation-sector module linked to a regionally adjusted zip code-level input-output model. Because the participation model allows for non-constant marginal utility, primary and secondary impacts exhibit nonlinear responses to variations in trip attributes. The modeling approach is demonstrated in an application to the saltwater sport fisheries for Pacific halibut and salmon in Lower and Central Cook Inlet, Alaska.

Testing for loss of 222Rn from Pacific halibut ( Hippoglossus stenolepis) otoliths

Radiometric ageing of fish by measuring the disequilibrium of 210Pb/ 226Ra found in otoliths has been used by numerous researchers in over 15 different studies. The ultimate goal of the previous research has been to validate conventional ageing methods. If 222Rn, an intermediary between 226Ra and 210Pb, escapes from the otoliths, the radiometric age would be biased young. The goal of this study was to test for this bias using Pacific halibut ( Hippoglossus stenolepis) otoliths collected in 1960 and analyzed in 1997. If 222Rn loss occurred, the estimated radiometric age would be less than the 37 year span between collection and analysis. In comparison to other fish species, Pacific halibut otoliths were found to have an unusually low activity of 210Pb and 226Ra. Low activity measurements lead to radiometric age estimates with very large estimated errors. All estimated radiometric ages for the Pacific halibut otoliths were much greater than 37 years. This suggests that 222Rn is not escaping from the otoliths and that radiometric ages are not biased low. However, considering the estimated error, the results are not definitive. This study should be repeated using a different species that is known to have a higher activity of 210Pb and 226Ra.