Horodysky and Graves: Estimation of survival of Tetrapturus albidus caught and released in the North Atlantic recreational fishery 87 



otherwise, they were left in the fish and the leader was 

 cut as close to the animal as possible prior to release. 

 Both practices are common in the recreational billfish 

 fishery. After capture and positioning alongside tagging 

 vessels, six white marlin were observed to have lost color, 

 and were lethargic and unable to maintain vertical posi- 

 tion in the water. These fish were resuscitated alongside 

 the moving boat for 1-5 minutes prior to release — also 

 a common practice in the recreational fishery. 



Gear type, fight time, handling time, fight behav- 

 ior, hooking location, overall fish condition, estimated 

 weight, and GPS coordinates of the release location 

 were recorded for each tagged white marlin. Fight time 

 was defined as the interval from the time the fish was 

 hooked to the time it was "leadered" alongside the boat 

 prior to tagging. Handling time included tagging and 

 resuscitation, if applicable. In accordance with Prince 

 et al. (2002a), straight-shank ("J") hooks were defined 

 as those with a point parallel to the main hook shaft, 

 whereas circle hooks were defined as having a point 

 perpendicular to the main hook shaft. All circle and 

 straight-shank ("J") hooks were rigged with dead bal- 

 lyhoo (Hemiramphus brasiliensis) bait. Size 7/0 Mustad 

 straight-shank ("J") hooks (models 9175 and 7731) were 

 rigged with the hook exiting the ventral surface of the 

 ballyhoo. Two models of circle hooks were employed in 

 this study: Mustad Demon Fine Wire (model C39952BL, 

 size 7/0; 5° offset, «=9) and Eagle Claw Circle Sea 

 (L2004EL, sizes 7/0-9/0; non-offset, n = ll). All circle 

 hooks were rigged so that they pointed upwards from 

 the head of the ballyhoo (see Prince et al., 2002a). The 

 rigging designations and fishing techniques unique to 

 each hook type were maintained in our study to reflect 

 the usual application of circle and straight-shank ("J") 

 hooks in the white marlin recreational fishery. Other 

 than these differences, all handling, tagging, and re- 

 cording methods were the same for both treatments. 



Hooking locations were pooled into two categories: 

 jaw, externally visible (including all lip-hooked, foul- 

 hooked, and bill-entangled white marlin) and deep, not 

 externally visible (including all white marlin hooked 

 in the palate, gills, esophagus, and everted stomachs). 

 Bleeding was recorded as present or absent, and the 



general location of bleeding was recorded when it was 

 possible to identify the source. 



Data analysis 



Survival of released white marlin was determined from 

 two distinct lines of evidence provided by the satellite 

 tags: net movement, and water temperature and depth 

 profiles. Time series of water temperature and depth 

 measurements taken about every 2 minutes (5-day tags) 

 or 4 minutes (10-day tags) were used to discriminate 

 surviving from moribund animals. Net movement was 

 determined as a minimum straight line distance trav- 

 eled between the coordinates of the initial tagging event 

 and the coordinates of the first reliable satellite contact 

 with the detached tag (inferred to be the location of 

 tag pop-up) derived from Argos location codes 1, 2, or 

 3 for the first or second day of transmission. In cases 

 where tags did not report more precise location codes, 

 an average of all location code readings for the first 

 day of transmission was used as a proxy for the loca- 

 tion of the tag pop-up. To determine the directions (and 

 magnitudes) of observed surface currents in areas where 

 fish were tagged, GPS coordinates (Argos location codes 

 of 1, 2, or 3, or a daily mean of location code 0, for tags 

 lacking these) were plotted for the 7-10 days that the 

 tags were floating at the surface and transmitting data 

 to satellites. Maps, tracks, and distances were generated 

 by using MATLAB (version 6.5, release 13.1, Mathworks 

 Inc, Natick, MA). 



Cochran-Mantel-Haenszel (CMH) tests were used 

 to address the effect of circle and straight-shank ("J") 

 hooks on survival, hooking location, and the degree 

 of hook-induced trauma. A Yates correction for small 

 sample size was applied when expected cell values were 

 less than 5 (Agresti, 1990). The effects of fight time 

 and total handling time on survival were assessed with 

 Wilcoxon-Mann-Whitney exact tests, with the null hy- 

 pothesis that there was no difference between surviving 

 and moribund white marlin. All statistical analyses 

 were conducted by using SAS (version 8, SAS Institute, 

 Cary, NC). The lone nonreporting tag observed in our 

 study was excluded from all subsequent analyses. 



