Assessing discard survivability and the physiological effects to capture on four skates species within the Northwest Atlantic
Historically skates within the northwest Atlantic were considered bycatch and discarded due to their low commercial value; however, landings exponentially increased following the establishment of an independent skate fishery in the 1990’s.
Unfortunately, this fishery was promoted before any regulations or life history data was known to help monitor skate populations and ensure stock sustainability. Despite the establishment of a fisheries management plan in 2003, biomass of the thorny (Amblyraja radiate) and smooth (Malacoraja senta) skates has not increase despite a complete ban from commercial retention. Additionally, winter skate (Leucoraja ocellata) biomass has decline by nearly 50% and the little skate (Leucoraja erinacea) is near the overfishing threshold and could potentially become overfished.
Understanding variable rates of capture-associated mortality are essential and may help to explain the current status among these aforementioned skate species. The objective of my master’s research is to is to quantify rates of immediate and short-term (delayed) mortality among the little, smooth, winter and thorny skates following capture by otter trawl and sink gillnet. Currently, 600 skates have been monitored and no immediate mortality has been observed in any species despite a wide range of capture conditions, prolonged tow time, and large cod-end biomasses. However, delayed mortality rates following trawl capture appear to vary among species with the highest and lowest mortality rates observed in the smooth and little skates respectively.
In addition to physical trauma, commercial capture events can severely disrupt homeostasis, creating a variety of physiological stresses that may further impact survivability. Previous research has established that capture stress can be lethal in fishes, however, compensatory responses vary greatly among species preventing generalizations to be made. In particular, skates often remain on deck for extended periods of time as the remaining catch is sorted and highly-valued fish such as Atlantic Cod are processes.
To better understand how the aforementioned skate species cope with and recover from various bout of air exposure both extra and intracellular mechanisms will be examined including, parameters such as pO2, pCO2, HCO3-, lactate, and heat shock proteins.
Venous whole-blood samples were obtained from little and thorny skates subjected to three different air-exposure durations (0, 15, and 50 minutes) in a laboratory setting. Based on preliminary results, it is clear little skates have a high threshold for coping with exposure to air, and can resolve seemingly large physiological disturbances from prolonged exposure. Data from additional skate species (thorny, winter and smooth) are presently being assessed according to the same treatments. Data on the nature and threshold for coping with air exposure by species can have considerable influence on regulatory fishing measures.