Abundance and Survival of Lingcod at Cape Flattery, Washington

Abstract

Using mark-recapture and fishery data from 1986 to 1992, I estimated abundance, survival, mortality, net loss, and catchability of lingcod Ophiodon elongatus in the nearshore waters of Cape Flattery, Washington. I used an open-population estimation model, which employed a multiple-year tag-release experimental design and an exploitation-based (sport fishery) tag-recapture process. The results indicated a high rate of population turnover (recruitment and emigration). Lingcod abundance appeared to vary in response to recruitment and ranged from 114,000 to 208,000 fish annually. Annual survival (5) ranged from 34 to 81%. Total instantaneous mortality (Z) was partitioned into sport fishing mortality (F) and a net loss term (L), which included both natural mortality and emigration; F ranged from 0.08 to 0.13 and L ranged from O.I I to 0.96. I propose that emigration is the best explanation for the high loss rates observed. Average catchability (q) declined by 60% from April to August, suggesting that reduced availability occurred seasonally at the nearshore area in late spring and summer. The results indicate the dynamic nature of the lingcod population near shore and the importance of modeling this stock as an open population for fisheries management.

Discard Mortality of Trawl-Caught Lingcod in Relation to Tow Duration and Time on Deck

“…Lingcod is one of the more resilient species studied. Our re-sults match well with other studies using lingcod exposed to air in either hook and line fisheries (Jagielo 1995;Albin and Karpov 1998) or laboratory simulations (Davis and Olla 2002;Schreck, unpublished data). Discard mortality may be magnified under various combinations of factors such as air temperature, water temperature, and the weight of the catch.…”

“…One hooking mortality study that examined recreational fishing mortality in California found very low levels of mortality after fish were held in tanks for several weeks (Albin and Karpov 1998). Consequently, their postrelease survival is thought to be generally good in recreational fisheries (Jagielo 1995(Jagielo , 1999. However, the vast majority of lingcod discards occur in the commercial bottom trawl fishery (PFMC 1999), and mortality rates for that gear type have never been estimated and so cannot be incorporated into stock assessment models (Jagielo et al 1997(Jagielo et al , 2000.…”

Movement, Mortality, and Size Selectivity of Sport- and Trawl-Caught Lingcod off Washington

“…The preopercular plate was marked with a plastic-coated wire spaghetti tag. Previous double-tagging and short-term-holding experiments indicated that tag loss and tag-related mortality with this procedure were negligible (Jagielo 1995).…”

“…Interestingly, this study found relatively greater selectivity of small female lingcod by the trawl fishery than was observed from a previous catchat-age analysis (Jagielo 1994) ( Figure 5). This discrepancy could be due to the discarding of small untagged fish and retention of small tagged fish as was previously reported to occur in the sport fishery at Cape Flattery (Jagielo 1995). Clearly, any unaccounted-for discard mortality will contribute to stock assessment error.…”

“…Previous mark-recapture studies of lingcod in the nearshore area at Cape Flattery, Washington, have indicated an open population with emigration (Jagielo 1990(Jagielo , 1995. Although few tagged fish released at Cape Flattery were recovered by fisheries operating in the inland marine waters of Puget Sound, significant numbers were recaptured on the trawl grounds off the Washington coast.…”