In iantaylor-NOAA/Lingcod_2021: Estimate the Status of Lingcod off the US West Coast in 2021

Life history

Geography

r Spp are large opportunistic predators endemic to the North Pacific (Figure \@ref(fig:map)), ranging from the Gulf of Alaska to central Baja California, Mexico [@wilby1937ling; @hart1973pacific]. Typically, the center of abundance can be found off the coasts of British Columbia and Washington State [@hart1973pacific]. r Spp are demersal on the continental shelf, display a patchy distribution, and are most abundant in areas of hard bottom with rocky relief [@rickey1991geographical]. They typically occur at depths less than 200 m but are caught in the \Gls{s-wcgbt} up to depths of 450 m.

Growth and maturity

r Spp are sexually dimorphic, with females typically growing faster and attaining larger asymptotic sizes than males [@richards1990multivariate]. Females also reach maturity at larger sizes [@cass1990lingcod; @miller1973fish] than males. Both males and females exhibit a latitudinal trend in growth, longevity, and size at maturity. Consequently, individuals from northern waters generally grow faster, live longer, and mature at larger sizes than individuals from southern regions [@richards1990multivariate; @silberberg2001analysis; @lam2019geographic].

r Spp are iteroparous spawners. Male r spp aggregate in late fall and move to rocky habitat in intertidal waters to depths of up to 126 m [@giorgi1981environmental; @o1993submersible] where they guard areas suitable for spawning. This movement has been correlated with a decline in the proportion of males in offshore trawl landings in late fall off California [@miller1973fish], British Columbia [@cass1990lingcod], and Washington [@jagielo1994assessment]. Mature females are rarely seen on the spawning grounds and appear to move from deep-water habitats into spawning areas only for a brief period to deposit eggs [@giorgi1981environmental]. Larger and older females appear to spawn first [@cass1990lingcod], depositing up to 500,000 eggs in high current areas [@hart1973pacific; @low1978study]. After fertilization, males guard clutches until the eggs hatch in six to eight weeks [@king2005male; @withler2004polygamous], between January and June [@jewell1968scuba; @low1978study]. Recent maturity studies suggest that r spp are batch spawners with the ability to spawn year round (pers. comm., M. Head, \gls{nwfsc}). Peak spawning takes place during October through December.

At hatching, r spp larvae are about 12 mm in total length and are epipelagic for approximately 90 days, until reaching about 70 mm and settling to soft bottom habitats [@phillips1977early; @cass1990lingcod; @hart1973pacific]. Epipelagic larvae feed on small copepods and copepod eggs, shifting to larger copepods and fish larvae as they grow [@phillips1977early]. \Gls{yoy} typically recruit to sandy, low-relief habitat near eelgrass or kelp beds, staying on soft bottom until they grow to at least 350 mm in length. After reaching 350 mm, they move into rocky, high-relief substrate, which is the preferred adult habitat [@petrie2006hunger; @bassett2018lingcod].

Newly settled juveniles are typically found at depths ranging from 9-55 m [@phillips1977early; @miller1973fish; @coley1986juvenile]. They often start in nearshore areas of sandy substrate [@buckley1984enhancement], move to a wider range of flat bottom areas by September [@cass1990lingcod], and then move into habitats of similar relief and substrate inhabited by adults while ages one to two but remain at shallower depths. Off the coast of California, they tend to initiate this latter move starting at around 35 cm in length [@miller1973fish]. Whereas, off the coast of Washington, juveniles have been found in hard bottom shell-cobble habitat near rocks in 9-15 m of water off the coast of Grays Harbor as soon as October [@coley1986juvenile].

Juvenile density in trawlable habitats tends to be higher in the south than in the north [@tolimieri2020SpatioTemporal]. Particularly, in central California shelf waters (50-240 m) between $34^\circ$ N and $39^\circ$ N and, just north of Cape Mendocino and Cape Blanco between $41^\circ$ N and $43^\circ$ N, albeit at smaller densities. These results are based on the \Gls{s-wcgbt}, which has an inshore limit of 55 m, and thus, the results do not account for potential differences in juvenile habitat in the north versus the south. Off of Washington, juveniles have been collected from the mouth of the Pysht River in the Strait of Juan de Fuca, Grays Harbor and Willapa Bay, and from coastal waters nearshore to these embayments [@buckley1984enhancement; @jagielo1994assessment].

Juvenile r spp feed on small fishes [@cass1990lingcod] including Pacific Herring (Clupea pallasii), Pacific Sand Lance (Ammodytes hexapterus), flatfishes (Pleuronectidae), Shiner Perch (Cymatogaster aggregate), Walleye Pollock (Theragra chalcograma), and an assortment of invertebrates including shrimps (Neomysis) and prawns (Pandalus). As juvenile r spp begin to move into rocky habitats and exceed 30 cm, other rocky reef bottomfishes become a more prominent component of their diet, making up 48.8\% of total prey biomass by weight [@beaudreau2007spatial].

Phillips and Barraclough [-@phillips1977early] estimated that \gls{yoy} growth was approximately 1.3 mm day$^{-1}$. Buckley et al. [-@buckley1984enhancement] reported \gls{yoy} growth from June to September in the Strait of Juan de Fuca also averaged 1.3 mm day$^{-1}$. Samples from the mouth of the Pysht River averaged 96 mm in June, 135 mm in July, 173 mm in August, and 200 mm in September [@jagielo1994assessment].

Habitat use

Outside of the spawning season, male and female r spp are segregated by depth. Females tend to inhabit deeper offshore waters, and males inhabit nearshore rocky reefs. Consequently, the sexes are vulnerable to different types of fishing gear. The majority of nearshore males (66.3\%) are caught using hook-and-line or spearfishing gear, and the majority of deep water females (62.4\%) are caught using trawl gear [@miller1973fish]. Fishery and survey data indicate that male r spp tend to be more abundant than females in shallow waters and the size of both sexes increase with depth [@jagielo1994assessment].

The movement and migration of r spp has been extensively studied through tag-recapture methods and acoustic arrays. As adults, r spp have a high [e.g., 95\%, Cass et al. -@cass1990lingcod; and 81\%, Jagielo -@jagielo1990movement] degree of site fidelity and tend to stay within an 8 km home range. Movement is apparent between coastal areas off Washington and southwest Vancouver Island but there is little interchange between these areas and the inland marine waters of Puget Sound and the Strait of Georgia [@cass1990lingcod; @jagielo1990movement]. However, some exceptional movements have been reported. For example fish tagged off of Cape Flattery, Washington were recaptured as far north as Queen Charlotte sound (195 km) and as far south as Cape Falcon (120 km) [@jagielo1990movement]. One fish tagged as a juvenile was recovered 510 km to the south in Oregon.

High site fidelity was also found using acoustic tags in Alaskan waters [@starr2005] and off of Central California [@greenley2009movements]. While r spp exhibit high site fidelity with an established location of residence, they frequently leave for 1-5 days traveling around 2 km to feed, only to return home for a longer duration. Large females generally had shorter residency times, spending more time outside of their tagged site. Additional acoustic studies in Prince William Sound reported that 50 cm individuals thought to be 2-4 years old disperse from nearshore reefs during spawning season, most likely due to displacement by older and larger spawning individuals [@bishop2010situ; @stahl2014examinationof]. Overall, residency times varied by sex, size, season, and habitat of residence.

Diet and trophic ecology

r Spp are top-order predators of the family r utils_name("Family"). Among the r utils_name("Family"), the genus r gsub("\\s.+", "", utils_name("latin")) is ecologically intermediate between the more littoral genera Hexagrammos and Oxylebius and the more pelagic Pleurogrammus [@rutenberg1962system].

Being opportunistic predators, r spp feed on a variety of fishes (pelagic and demersal), cephalopods, and crustaceans [@wilby1937ling]. Their feeding strategies are known to vary with depth of occurrence, latitude, sex, and size (pers. comm., B. Brown, \gls{mlml}). Geographic variation in trophic level is associated with oceanographic factors such as sea-surface temperature or chlorophyll-a density that likely corresponds to shifts in prey availability, suggesting a similar shift in the predatory role of r spp in coastal environments.

Male r spp caught in shallow depths have more diverse diets and consume more prey items that are of a lower trophic level (e.g,. cephalopods) than females caught in deep depths that have less diverse diets and consume more prey items that are of a higher trophic level (e.g., groundfishes). Preliminary observations from r spp stomach contents sampled from Washington to California in both nearshore and offshore habitats indicate a higher occurrence of bony fishes in the diet of northern fish than those collected off of California (pers. comm., B. Brown, \gls{mlml}). Fish collected off of California and southern Oregon had a higher occurrence of cephalopods in their diet than fish collected from more northern waters. This latitudinal shift in prey composition suggests differences in feeding behavior and the predatory role of r spp in coastal environments. Being opportunistic feeders, it is not a surprise that rockfish biomass in the r spp diet increases by three-fold for r spp found inside marine reserves compared to those found outside of reserves [@beaudreau2007spatial].

Stock delineation

Longo et al. [-@longo2020strong] used restriction-site associated deoxyribonucleic acid sequencing techniques and discovered evidence for distinct north and south genetic clusters with the presence of admixed individuals (i.e., mixes of previously diverged or isolated genetic lineages) in the region of overlap. Pure northern-cluster individuals represented over 80\% of the samples at $42.2^\circ$ N and all sampled sites that were further to the north. Pure southern-cluster individuals represented over 80\% of the samples at all sampled sites south of $35.2^\circ$ N. Only two sites were sampled within the range where most admixed individuals were found, $38.6^\circ$ N and $39.5^\circ$ N. Thus, it was difficult to define a clean break between the clusters. The general results of the occurrence of two distinct genetic clusters were contrary to previous genetic work using mitochondrial deoxyribonucleic acid that found no genetic differentiation in the r spp population [@marko2007mtdna].

The recent genetic results concurred with results from recent work demonstrating that r spp growth, longevity, and timing at maturity exhibit a latitudinal gradient. r Spp from higher latitudes are larger at age (Figure \@ref(fig:Lam-vbgfcurves)), live longer, and reach biological maturity at larger sizes (Figure \@ref(fig:age-mat-forassessment)) compared to conspecifics from lower latitudes (Lam et al. -@lam2021geographic; pers. comm., M. Head, \gls{nwfsc}).

This known variability in life-history parameters and genetic structure led to the reexamination of the previous stock boundary used for r spp, located at the California - Oregon border [@hamel2009lingcod; @haltuch2019lingcod]. A break point at Cape Mendocino, California ($40^\circ 10^\prime$ N) was chosen for this assessment because it (1) falls within the mixing zone of the two genetic clusters, (2) falls in the vicinity of where the greatest difference in r spp size-at-age was detected (Figure \@ref(fig:Lam-vbgfcurves)), and (3) aligns with the federal management boundary for commercial quotas and a boundary between two \Gls{cdfw} management regions, which facilitates the application of assessment results for future management and separation of historical catch.

iantaylor-NOAA/Lingcod_2021 documentation built on Oct. 30, 2024, 6:42 p.m.