582 



No evidence of bias from fish behavior in 



the selectivity of size and sex of 



the protogynous red porgy 



iPagrus pagrus, Sparidae) by hook-and-line gear 



Douglas A. DeVries 



Email address: doug.devrles@noaa,gov 



National Oceanic and Atmospheric Administration 



National Manne Fisheries Service 



Southeast Fishenes Science Center 



Panama City Laboratory 



3500 Delwood Beach Road 



Panama City Flonda 32408 



Most fisheries select the size of fish 

 to be caught (are size selective), and 

 many factors, including gear, market 

 demands, species distributions, fish- 

 ery laws, and the behavior of both 

 fishermen and fish, can contribute 

 to that selectivity. Most fishing gear 

 is size-selective and some, such as 

 gill nets, are more so than others. 

 The targeting behavior of fishermen 

 is another key reason commercial 

 and recreational fisheries tend to be 

 size-selective. The more successful 

 fishermen constantly seek areas and 

 methods that yield larger or more 

 profitable sizes offish. Fishery regu- 

 lations, especially size limits, produce 

 size-selective harvests. Another factor 

 with the potential to cause selectivity 

 in a hook-and-line fishery is the dif- 

 ferent behavioral responses of fish to 

 the bait or lure, whether the different 

 responses arise among different fish 

 sizes or between the sexes. 



There is reason for concern over 

 the effect of size-selective fishing on 

 protogynous species, i.e., sequential 

 hermaphrodites, which begin life 

 as females and later change sex to 

 males. In one way, size-selective 

 fishing affects gonochoristic (sexes 

 separate) and protogynous species 

 similarly: it not only reduces num- 

 bers, but also truncates size distri- 

 butions. These effects can result in 

 earlier maturation at smaller sizes 

 and hence, at the very least, a re- 

 duction in individual fecundity (J0r- 

 gensen, 1990). Size-selective fishing 

 can, however, uniquely affect protog- 



ynous species in at least two other 

 ways. Because there is essentially a 

 second maturation when sex change 

 occurs, barring some compensatory 

 response, size-selective fishing is sex- 

 selective fishing. As exploitation re- 

 moves the larger and primarily male 

 members of the population, sperm 

 limitation and decreased fertiliza- 

 tion rates can occur. These effects 

 could be caused by a reduction in the 

 number of males or because rapidly 

 skewed sex ratios disrupt the social 

 cues for mating (Bannerot et al., 

 1987; Huntsman and Schaaf, 1994; 

 Coleman et al., 1996). Naturally low 

 sex ratios can decline precipitously in 

 some heavily fished protogynous spe- 

 cies, especially those that form large, 

 temporally and spatially, predictable 

 spawning aggregations (Coleman et 

 al., 1996). The second potential effect 

 of size-selective fishing that is unique 

 to protogynous species is a decrease 

 in population fecundity (Vincent and 

 Sadovy, 1998), which could accom- 

 pany a compensatory drop in size at 

 sex change, because this drop in size 

 would essentially equate to increased 

 mortality on the largest, most fecund 

 females (Shepard and Idoine, 1993). 

 Such an effect, however, would only 

 occur if at least some females were 

 initially included in the exploited 

 portion of the population. 



The documented responses of pro- 

 togynous species to fishing have var- 

 ied. Significantly, fewer male dag- 

 gerhead seabream iChrysoblephus 

 cristiceps) and Roman seabream (C. 



laticeps), both sparids, were found in 

 areas open than in areas closed to 

 fishing — a finding attributed to se- 

 lective removal of larger size classes 

 (Buxton, 1993). In contrast, the aver- 

 age size and age of male leopard cor- 

 algrouper (Plectropomus leopardus), a 

 serranid, were not consistently small- 

 er, nor was the sex ratio consistently 

 more female-biased in areas open to 

 fishing than in closed areas (Adams 

 et al., 2000). 



Recent significant declines in the 

 modal sizes and proportions of males 

 of gag (Mycteroperca microlepis) and 

 scamp (M. phenax) — both serranids 

 and protogynous species — in the Gulf 

 of Mexico (GOM) were likely due to 

 size-selective or sex-selective har- 

 vesting, or both, that was affected by 

 fish behavior (Coleman et al., 1996). 

 Among gag, the proportion of males 

 fell from 17% during 1977-80 (Hood 

 and Schlieder, 1992) to 1.3-2.7% dur- 

 ing 1991-93 (Coleman et al., 1996) 

 in the GOM, and from 19.6% during 

 1976-82 to 5.5% in 1995 in catches 

 from U.S. Atlantic waters (McGovern 

 et al., 1998). Coleman et al. (1996) 

 cited Gilmore and Jones (1992) for 

 their conclusions about behavior-re- 

 lated selectivity in scamp and per- 

 sonal observations by Gilmore for 

 similar conclusions regarding gag. 

 Gilmore and Jones (1992) speculated 

 that the bias towards large males 

 that they noted in hook-and-line col- 

 lections of gag and scamp was related 

 to the more aggressive behavior and 

 greater movement of males, and the 

 higher position of males in the water 

 column. Even though these are the 

 only protogynous species in which 

 behavior-related size or sex selectiv- 

 ity has been documented (and only 

 by observations, not experiments), 

 the shift in size and sex ratio in gag 

 has often been cited as an example of 

 how a species with this kind of mat- 

 ing system responds to exploitation 

 (Vincent and Sadovy, 1998). 



The objective of the present study 

 was to determine if there was any 



Manuscript submitted 9 June 2006 

 to tlie Scientific Editor's office. 



Manuscript approved for publication 

 15 July 2007 by the Scientific Editor. 



Fish. Bull 105:582-587. 



