NOTE DeVnes: No evidence of bias from fish behavior in the selectivity of size and sex of Pagrus pagrus by hook-and-llne gear 



585 



of males and number of females); therefore these 

 four collections could not be tested. 



Discussion 



The absence of any evidence of behavior-related 

 size or sex selectivity indicates that hook-and-line 

 sampling can provide reasonably unbiased infor- 

 mation on the population biology and stock status 

 of red porgy. As hook size approaches the extremes, 

 vulnerability will decrease and bias will increase, 

 and therefore choice of hook size is critical. There 

 is evidence in some reef fishes that, across at least 

 a moderate range of hook sizes, selectivity can be 

 relatively constant (Ralston, 1982; Dalzell, 1996). 

 Size-1 Mustad j-style hooks were chosen for this 

 study on the basis of considerable experience of 

 the author in catching many species of reef fishes 

 in the study area — experience that indicated that 

 such hooks would readily catch all sizes of red 

 porgy typically observed in both recreational and 

 commercial catches in the GOM. During the study, 

 red grouper (Epinephelus morio) that were much 

 larger than the largest red porgy collected and that 

 had considerably larger gapes were caught on the 

 same hooks, as were many tomtates [Haemulon 

 aurolineatum) which were similar in size and had 

 similar gapes as the smallest red porgies caught. 



A critical assumption of this study was that all 

 sizes of red porgy present at a location when a 

 given sample was collected were equally vulner- 

 able to the gear. If, because of gear selectivity, smaller 

 individuals were considerably less vulnerable than 

 larger ones, and significant numbers of small fish were 

 present at a site being sampled, then it would be pos- 

 sible for behavior-related selectivity for larger fish to 

 occur undetected, or at least its magnitude would be 

 underestimated. 



Several lines of evidence indicate that the aforemen- 

 tioned scenario is very unlikely. Size data from the 

 eastern GOM, collected during recent annual National 

 Marine Fisheries Service (NMFS) reef fish surveys 

 with the use of stationary video cameras equipped 

 with laser measuring devices, showed no evidence of 

 noticeably greater proportions of small fish than those 

 seen in the hook-and-line samples of the present study 

 (Fig. 1). Although the size distributions were statisti- 

 cally different (Kolmogorov-Smirnov 2-sample test, 

 P<0.001) — not surprising given the very large sample 

 sizes — the primary difference appeared to be that the 

 distribution of red porgy sizes shown in the video data, 

 which should have had little or at least much less bias, 

 was shifted towards larger, not smaller fish. Although 

 a few (3.6%) individuals in the video data were smaller 

 than the smallest (193 mm TL) in the hook-and-line 

 samples, it is important to note that the proportion 

 of large fish (>360 mm) was almost 10-fold greater 

 than in the hook-and-line samples, i.e., 21.69c versus 

 2.5%. Thus, if anything, the size distribution in the 



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Order of capture 



Figure 2 



Plots of individual red porgy {Pagrus pagrus) size (upper 3 

 panels) and sex (lower three panels I in the order they were 

 captured for three selected collections. The right hand column 

 indicates the sampling site and date of capture. See Figure 

 3.1 in DeVries (2006) for site details. Transitional-stage fish 

 were considered males. M = males, F = females. 



hook-and-line data is biased downwards, not upwards. 

 The higher proportion of larger fish in the video data 

 probably reflects spatial and bathymetric differences 

 in the sampling more than different gear selectivities. 

 The video survey focused on the hard bottom, high- 

 relief habitat along the 73-m (40-fathom) isobath and 

 inshore of that isobath in the Florida Middle Grounds. 

 In contrast, all fish in the present study were caught 

 between 41 and 67 m and on low-relief habitat. Larger 

 red porgy have been found in deeper water and in the 

 Florida Middle Grounds (Harris and McGovern, 1997; 

 Hood and Johnson, 2000). 



Red porgy size-structure data from the NMFS recre- 

 ational headboat survey collected during 1999-2001 in 

 northwest Florida and Alabama almost mirrored the 

 data from this study (Fig. 1). The headboats regularly 

 catch red snapper iLutjanus campechanus) as large 

 as or larger than the largest red porgy taken in this 

 study, and their fishing grounds completely overlap 

 the area, depths, and habitats sampled in the present 

 study. If significant numbers of red porgy larger than 

 those collected in the present study inhabited the area 

 sampled in this study, it seems very unlikely they would 

 not show up in the NMFS survey samples of headboat 

 catches from the same region. Larger red porgy are in 

 fact caught regularly by headboats fishing the Florida 

 Middle Grounds off the central west coast of Florida 

 (Hood and Johnson, 2000). 



