For each sampling event, defined as a day on which actual fishing took place, two to four vessels utilized commercial bottom set longline gear and rod and reel to target cod. After capture, sub-legal cod (<22 inches) were evaluated and held in on-board live wells until 50 fish had been collected, constituting a replicate, and the vessel was prepared for caging. The fish were then lowered to the seafloor in cages that were retrieved and evaluated after at least 72 hours. Fishermen were responsible for determining suitable experimental fishing areas within each required season-depth strata.
Strata: Fish were collected during the winter, spring, summer and fall seasons.The main variable of concern from season to season was sea surface temperature and therefore aimed to sample in each of four temperature categories as follows:
Cold (<= 43 F)
Cool (44-48 F)
Warm (49-58 F)
Hot (> 58 F)
The study was also designed to assess survival across different capture depths, and to investigate the interplay between season and depth. The statement of work called for sampling to take place in 20, 30, and 40 fathoms. This range represents the depths where most regional longline fishing occurs (J. Pappalardo, P. Comm.). The only change to the protocol in this respect was to treat these categories as ranges as follows:
20 fathoms 15-25 fathoms
30 fathoms 25-35 fathoms
40 fathoms 35-45 fathoms
Treatments: Within each unique combination of season and depth, three different treatments were conducted: snubbed, unsnubbed, and jigged. Snubbed and unsnubbed were both taken off the demersal longline gear and were intended to duplicate as closely as possible the release (discard) conditions for normal commercial fishing. As such, these treatments were comprised of the first 50 fish caught off a given string regardless of condition. While dead fish might not be tanked or caged to avoid attracting scavengers, they were still counted as mortality towards the sample size. The jigged fish were intended to act as a control, which would indicate cage-induced mortality. As such, only strong fish with no major injuries were selected towards the 50 fish sample; dead, weak or injured fish were not used or counted.
For each season, a minimum of 150 sub-legal fish were targeted for each of the three treatments at each of the three different depths.
NOTE: The 6/21/04 fish suffered from lack of oxygen while held on deck (first warm water sampling). Subsequent samples had bubblers and ice packs to keep the deck water cool and oxygenated.
For in-depth details on sampling protocols, see the final report.
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