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Influence of Bait Type on Catch Rates of Predatory Fish Species on Bottom

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Influence of Bait Type on Catch Rates of Predatory Fish Species on Bottom 50 Abstract—Identifying effective methods of reducing shark bycatch Influence of bait type on catch rates of in hook-based fisheries has received predatory fish species on bottom longline little attention despite reports of declines in some shark populations. gear in the northern Gulf of Mexico Previously proposed shark bycatch mitigation measures include gear 1 modifications, time and area clo- William B. Driggers III (contact author) sures, avoidance of areas with high Matthew D. Campbell1 shark abundance, use of repellents, Kristin M. Hannan2 and use of specific bait types. Re- 1 gardless of the method of shark by- Eric R. Hoffmayer catch reduction, knowledge of the Christian M. Jones1 effects of the chosen method on the Lisa M. Jones1 catch rates of targeted fish species Adam G. Pollack2 should be understood. To examine the effects of bait type on catch rates of sharks and teleosts on bot- Email address for contact author: [email protected] tom longline gear, standardized gear was deployed with bait alternating 1 Mississippi Laboratories between Atlantic mackerel (Scomb- Southeast Fisheries Science Center er scombrus) and northern shortfin National Marine Fisheries Service, NOAA squid (Illex illecebrosus). For all P.O. Drawer 1207 shark species examined, except the Pascagoula, Mississippi 39567 scalloped hammerhead (Sphyrna 2 Riverside Technology Inc. lewini), a preference for hooks baited Mississippi Laboratories with Atlantic mackerel was observed. Southeast Fisheries Science Center Commercially and recreationally im- National Marine Fisheries Service, NOAA portant teleosts had no significant P.O. Drawer 1207 preference for a specific bait, with Pascagoula, Mississippi 39567 the exception of the red drum (Sci- aenops ocellatus), which had a sig- nificant preference for hooks baited with northern shortfin squid. Bait preference decreased as total catch rate increased on individual longline Because of reported declines in (Ward et al., 2008), reductions in sets. Our results point to the use of some shark populations, there has gear soak time (Carruthers et al., specific baits as a viable method to been increasing interest in mitigat- 2011), adjustments in fishing depth reduce shark catch rates without de- creasing catches of targeted teleosts. ing bycatch rates of shark species in (Rey and Muñoz-Chápuli, 1991), time longline fisheries that target teleosts and area closures (Watson et al., (Francis et al., 2001; Beerkircher et 2009), avoidance of areas of known al., 2002; Gilman et al., 2008; Ward high shark abundance (Walsh et al., et al., 2008). Within the northern 2009), use of repellents (Robbins et Gulf of Mexico, commercial fishing al., 2011) and use of specific bait for sharks has occurred since the types (Gilman et al., 2007). Ultimate- 1920s (Rogers, 1920) and continues ly, for any bycatch reduction method to present day. Although directed to be fully embraced within a fishery, commercial fishing effort for sharks it will be necessary that catch rates Manuscript submitted 10 November 2015. in the region has waxed and waned of targeted species not be negatively Manuscript accepted 27 October 2016. over the years, shark bycatch con- affected when a specific approach is Fish. Bull. 115:50–59 (2017). tinues to be an important source of applied. Ideally, a bycatch reduction Online publication date: 10 November 2016. mortality, particularly in hook-based approach would minimize bycatch doi: 10.7755/FB.115.1.5 fisheries, such as the snapper and rates and not affect catch rates of The views and opinions expressed or grouper bottom longline fishery (e.g., target species and cause the least implied in this article are those of the Scott-Denton et al., 2011). amount of economic hardship and author (or authors) and do not necessarily Proposed or enacted efforts to cur- changes to proven fishing practices. reflect the position of the National tail shark bycatch in longline fisher- Among measures proposed to miti- Marine Fisheries Service, NOAA. ies have included gear modifications gate shark bycatch, use of bait that Driggers et al.: Influence of bait type on catch rates of predatory fish on longline gear 51 does not decrease catch rates of target species yet re- to be different from the positions that were originally duces rates of shark capture could be the most easily planned. The bounds of the sampling universe were se- implemented and likely to be readily accepted within lected to maximize sampling opportunities within tem- a fishery. poral limitations. Past studies have shown that catch rates of certain Bottom longline gear consisted of 1842 m of 4.0-mm shark species are affected by the use of specific bait monofilament mainline and 100 gangions. Each gan- types. For example, Gilman et al. (2007) analyzed data gion was 3.7 m in length and constructed of an AK snap collected in the pelagic longline fishery in Hawaii and (size 150), 3.2 m of 3.0-mm-diameter monofilament, 0.5 determined that the catch rate of blue sharks (Priona- m of 2.4-mm-diameter fishing wire, and a 15/0 circle ce glauca) was reduced by 36% when fish, rather than hook (Mustad #39960D1, O. Mustad & Son A.S, Gjörvik, squid, were used as bait. Similarly, Watson et al. (2005) Norway). Each gangion was baited with Atlantic mack- conducted experimental longline sets in the western erel (Scomber scombrus) or northern shortfin squid (Il- North Atlantic Ocean and found catch rates of blue lex illecebrosus). Both bait types were cut so that they sharks were 31–40% (depending on hook type) lower were of the same approximate dimensions and appro- on hooks baited with fish than on hooks baited with priately sized for the hook. Gangions were deployed so squid. Although results of these studies are potentially that each bait type alternated along the length of the biased by use of multiple hook types and sizes, their mainline (i.e., northern shortfin squid, Atlantic mack- results strongly indicate that use of a specific bait type erel, northern shortfin squid, Atlantic mackerel), and could be a means to reduce bycatch of sharks. the starting bait type was selected randomly for each Hook-based fisheries in the northern Gulf of Mexico longline set. that target grouper (Serranidae), snapper (Lutjani- Gear soak time, defined as time elapsed between de- dae), and tilefish (Malacanthidae) species frequently ployment of the terminal high flyer during gear deploy- capture sharks (Gulak et al., 2013). For example, the ment and retrieval of the first high flyer during haul- Atlantic sharpnose shark (Rhizoprionodon terraenovae) back, was approximately 1 h at sampling sites with was the sixth-most captured fish species among the ap- depths less than 400 m and 2 h at sampling sites with proximately 180 fish species reported in observer data depths greater than 400 m. However, the actual time collected from the bottom longline fishery for reef fish each hook spends in the water can vary due to a num- in the Gulf of Mexico (Scott-Denton et al., 2011). Fur- ber of factors, such as hook position along the mainline, thermore, smoothhound (Mustelus spp.) and blacknose differences in gear setting and retrieving speeds, and (Carcharhinus acronotus) sharks were among the 20 delays related to handling times that were associated most frequently captured fish taxa within the same with the number of organisms captured. Therefore, the fishery (Scott-Denton et al., 2011). The size and type time each hook entered the water at deployment and of hooks vary in the bottom longline fishery for reef exited the water during retrieval was electronically fish in the Gulf of Mexico (Gulak et al., 2013), and bait monitored. The elapsed time between deployment and type is inconsistent, depending on personal preference, retrieval of each hook was considered hook soak time. availability, and price, among other factors (Prytherch, The status of each retrieved hook was monitored 1983; Scott-Denton et al., 2011). Because there is high and recorded as whole bait present, partial bait pres- variability in the gear and bait used within this fish- ent, no bait present, missing hook, or organism cap- ery, use of observer data to examine potential effects of tured. To determine whether baits of Atlantic mackerel bait type on the catch rates of specific species is prob- and northern shortfin squid were retained equally on lematic. Our goal was to conduct a controlled experi- hooks, data from gangions classified with a status of ment to test the effects of 2 readily available bait types whole bait present were compared by using chi-square commonly used in the bottom longline fishery for reef tests with Yates correction for continuity. Using the fish on catch rates of sharks and economically impor- same test, we investigated potential differences in tant teleosts in this region. Additionally, we examined bait retention between Atlantic mackerel and northern density-dependent effects on preferences for the 2 bait shortfin squid when there were hook interactions with types for both groups of fish species. feeding organisms other than those retained on a hook. For this investigation, the categories partial bait pres- ent and no bait present were combined. We combined Materials and methods them because of the subjective nature of the partial bait present category (i.e., the status of a hook was Bottom longline gear was deployed from the NOAA classified the same whether, for example, a small piece Ship Oregon II at sampling sites in the northern Gulf of bait tissue had been removed or most of the bait of Mexico from 11 March through 13 April 2015. Sam- had been removed). The category missing hook was not pling sites were selected on the basis of 18.5-km grids included in analyses because, in the limited number within predefined geographic areas (from Pascagoula, of cases for which this status was recorded, the hook Mississippi, to Cape San Blas, Florida) and depth (9–1000 m) constraints.
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