This article originally appeared in The Shark Tagger-1997 Annual Summary
In 1997, APP personnel were fortunate to have four opportunities to go into the field to tag and inject porbeagle sharks for our ongoing age and growth study (see 1996 Shark Tagger Summary). Two of these trips were in the spring onboard the F/V Panther in the Gulf of Maine during regular commercial porbeagle fishing operations; tagging was done opportunistically. The other two were research cruises conducted in the fall specifically targeting porbeagle sharks. The results of these cruises are combined and summarized here.
The objectives of the porbeagle tagging cruises were to: 1) tag and inject porbeagle sharks with oxytetracycline (OTC) for migration and age and growth studies; 2) collect morphometric data; and 3) collect biological samples for age and growth, food habits, and reproductive studies.
Operations for all four porbeagle cruises were conducted between Mt. Desert Rock, ME and Cape Cod, MA, out to approximately 60 nm offshore. Surface temperatures in the spring varied, between 44° to 46° F, and depth ranged from 39 to 100 fm. In the fall, the surface temperatures ranged from 49° F to 66° F and depth ranged from 48 to 124 fm.
Pelagic longline sampling gear was set at each station. The gear configuration varied depending on time of day and area. The basic gear consisted of 900 lb monofilament mainline with 24 ft (7.3 m) gangions, although gangion type varied. Some were composed of monofilament line while others were composed of rope with wire leaders. The number of sets per day depended on the catch from previous sets and weather conditions.
In the spring, 32 sets of longline gear were completed. The majority of porbeagles caught on these trips were taken commercially, allowing us to sample the catch for biological studies. We measured fork lengths (FL) and took vertebrae for age and growth studies from 15 porbeagles. Reproductive dissections were performed on two porbeagles, and food habits dissections were completed on 12 sharks. Additionally, samples of spiral valves were taken from five porbeagles of varying sizes for parasite research, and samples of liver and muscle were taken for DNA studies. Sixteen porbeagles were tagged and injected with OTC for age validation studies during these cruises.
In the fall, 35 longline sets produced 583 sharks, representing 5 species. The majority of the sharks caught were blue sharks (420), followed by porbeagle (99), spiny dogfish (47), thresher (12) and mako sharks (5). Of these, 388 were tagged (384 blues, 93 porbeagles), four (porbeagles) were dissected, and 91 sharks were lost or released at the rail (this included 50 spiny dogfish released without tags). In all, 85 porbeagle, 53 blue, and two thresher sharks were injected with OTC.
These four cruises were invaluable to our current porbeagle shark research. Sharks have already been resumed and in one case, the whole vertebral column of an injected porbeagle was removed and sent to us (see Porbeagle Shark Age and Growth).