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Fishery Bulletin 103(4) 



weighted fishing lines. Multiple lines are mounted on 

 outrigger poles to ensure separation of the lines and 

 are controlled by small hydraulic winches (Starr et al., 

 1998). Depending on conditions, commercial fishermen 

 use three to fifteen lures per line and two to six lines 

 per boat, totaling six to ninety lures with hooks per 

 boat. In recreational boats each fisherman traditionally 

 uses one rod, reel, line, and hook with bait. 



Surface takes, also termed "definite takes," were de- 

 fined as takes when pinnipeds took a hooked salmon 

 (and when the species and number of marine mammals 

 involved could be determined). Surface takes were also 

 recorded when fish were hooked and the action of the 

 line indicated that a fish was no longer hooked, and a 

 pinniped surfaced immediately with a fish in its mouth. 

 Takes below the surface, or "probable takes," were de- 

 fined as takes when fish were removed from the hook 

 (and when the species and number of marine mammals 

 involved could not observed directly). Evidence that 

 indicated the occurrence of below-surface takes was in 

 the form of bent hooks, lost gear, or a sea lion surfac- 

 ing within several minutes with a salmon, provided no 

 other fishing boats were in close proximity. Two types of 

 takes were designated because takes below surface were 

 not witnessed, and other predators including sharks 

 take fish from lines, or fish may have escaped. However, 

 fishermen and researchers recognized that takes by 

 pinnipeds, specifically by sea lions, differed from takes 

 by sharks and other predators by the action of the line, 

 effect on the hook or lure (or both), and type of bite on 

 fish parts remaining on the hook. 



Number of salmon and percentage of catch taken by 

 pinnipeds were compared with the total catch and the 

 legal catch in commercial and recreational fisheries. To- 

 tal catch was defined as numbers offish hooked, includ- 

 ing all legal-size fish, fish taken by pinnipeds, and all 

 undersize fish. Legal catch represented only fish of legal 

 size landed by anglers. Our rationale for using total 

 catch was that all fish, regardless of size, have an equal 

 probability of being taken by pinnipeds; therefore, com- 

 parisons with total catch were a more accurate metric 

 for quantifying the impact of pinnipeds on the salmon 

 fishery. Comparisons with the legal catch inflated the 

 percentage of fish taken by pinnipeds and exacerbated 

 the perception of the problem of pinnipeds interacting 

 with salmon fisheries. However, previous researchers 

 have compared percentage takes by pinnipeds with legal 

 catch; therefore we also made the comparison with legal 

 catch to place our results in a historical context. 



Mean percentages of fish taken by sea lions in rela- 

 tion to total catch (referred to as "mean percentage of 

 fish taken by sea lions") for the commercial, CPFV, and 

 skiff fisheries for onboard and dockside surveys from 

 1997 to 1999 were non-normal in distribution and were 

 transformed by using the arcsine transformation for 

 parametric statistical comparisons (Zar, 1996). Mean 

 percentages of fish taken by sea lions in the three fish- 

 eries (commercial, CPFV, and skiff) were compared 

 between onboard and dockside surveys, among years 

 (1997 to 1999), between seasons (sea lion breeding and 



nonbreeding seasons), and between takes (surface and 

 below surface) using a Students t-test and ANOVA or 

 a Mann-Whitney [/-test and Kruskal-Wallis test for 

 data that were non-normal and heteroscedastic after 

 transformation. 



Sea lion breeding and nonbreeding seasons from 1997 

 to 1999 were determined by using aerial and ground 

 counts from Weise (2000). The breeding season was desig- 

 nated as the time when a significant decline in the num- 

 ber of breeding adult males was recorded at haul-out sites 

 in the Monterey Bay region, when animals where pre- 

 sumably heading for the breeding rookeries in southern 

 California. Typically the breeding season is from June 

 and July, and the nonbreeding season occurs during the 

 months of March, April, May, August, and September. 



Mean catch per unit of effort, or the numbers of fish 

 hooked per day per boat, in commercial, CPFV, and 

 skiff fisheries data were non-normal and heterosce- 

 dasti c, theref ore, were they were transformed by us- 

 ing -J count + 1 (Harvey, 1987; Zar, 1996). Mean catch 

 per unit of effort for the three fisheries was compared 

 among years with an ANOVA. 



To estimate the impact of California sea lion depreda- 

 tion on salmon populations in Monterey Bay we com- 

 pared estimated numbers of hooked salmon taken by 

 sea lions and the Central California Valley index (CVI) 

 for chinook salmon abundance. The CVI is the numbers 

 of ocean- and inland-harvested Chinook salmon and the 

 sum of all runs of chinook on the Sacramento Rivers 

 (PFMC 4 ) and represents presumably the population 

 of salmon passing through the Monterey Bay region 

 during the fishery season. The estimated number of 

 salmon taken was calculated from the observed num- 

 ber of takes in the commercial and recreational fishery 

 multiplied by the percentage of the total catch that was 

 sampled. Percentage of the total catch sampled was es- 

 timated by dividing the number of observed legal-size 

 fish landed by the total number of legal-size fish landed 

 (CDF&G, unpubl. data 7 ). 



Monetary losses resulting from sea lion interactions 

 with salmon fisheries were estimated by evaluating 

 numbers of fish taken by sea lions and types and quan- 

 tities of fishing gear damaged or lost during these inter- 

 actions. Information for the analysis of monetary loses 

 was collected during dockside and onboard surveys for 

 commercial and recreational salmon fisheries. 



Annual monetary losses resulting from fish taken 

 by sea lions were calculated by using total numbers 

 of estimated takes by sea lions, average dressed mass 

 (mass of gutted and cleaned fish) of salmon landed in 

 Monterey from 1997 to 1999, and average exvessel price 

 (wholesale price per pound of fish paid to fishermen) 

 for chinook salmon in California from 1997 to 1999 

 (PFMC 4 ). Estimated numbers of takes by sea lions in 

 Monterey Bay from 1997 to 1999 were a function of 



7 CDF&G (California Department of Fish and Game). 2004. 

 Ocean Salmon Project database. CDF&G Ocean Salmon 

 Project, 475 Aviation Blvd., Suite 130, Santa Rosa, CA 

 95403. 



