Blood, guts, and gore! Those words sound like a review for a horror movie, but it’s actually the basis of my field work. I’ve been looking at and evaluating a lot of fish guts for the Cooperative Research Branch Conversion Factor Project.
Giving Groundfish Conversion Factors a Refresh
Many fish are gutted at sea, which means the internal organs are removed to prevent spoiling. Once these fish are offloaded from a commercial trip, scientists apply a conversion factor to the gutted weight to convert it to a whole weight which they use to evaluate the abundance of a fish stock. As the ocean changes, fluctuations in temperature and shifting prey availability impact fish metabolism and physiology. That can cause changes in average fish size and weight.
The conversion factors used for cod, haddock, and pollock haven’t been updated since the 1960s, so they’re in need of a little refresh. That’s where I come in. I’ve been sailing on commercial groundfish vessels all over the region. The goal? Collect data that represents the landings of the commercial groundfish fleet from different ports, gear types, and gutting methods.
My mobile office changes from vessel to vessel as I bring everything I need to do my job back and forth each time. Sailing aboard commercial fishing vessels is not a 9–5 job. Sometimes we leave in the middle of the day, sometimes we leave in the middle of the night. In fact, the only consistency is that when the lines get thrown, everyone is quite literally in the same boat. I work with the captain and crew on each trip to find a space and establish a work flow that fits their deck space and fishing operations.
Weighing and Measuring Fish is not a Fair-Weather Job
Once there are fish on board, my work really begins. For each fish I sample, I typically record six different data points. I use a motion-compensated sea scale to measure the whole weight of an individual fish. Next, I place the fish on an electronic length board and use a magnet to ping the length directly into my field tablet. Once I have both the whole weight and length, I gut the fish (or send it through the gutting machine if the vessel has one). During this step, I assess the sex of the fish and maturity stage of the gonads. Sex and maturity status can result in fluctuations in the weight of the fish throughout the year. A fish that is ripe for spawning has a higher whole weight, as the reproductive organ, called a gonad, swells with eggs or sperm. This results in a greater whole weight-to-gutted weight ratio.
After I remove all the innards—including the liver, intestines, stomach and gonad—I weigh the fish once more. It then goes back on the length board where I measure the gutted length. This process is rinsed and repeated for each fish sampled over the course of many days at sea.
The best thing about this system is that all the data I collect is synced directly to my field tablet. This reduces errors that could be caused by transcribing data after the fact and allows me to sample greater volumes of fish at a faster pace. However, technology does not always pair well with wet environments and that is certainly true for my field tablet! Fishing doesn't stop if it’s raining or snowing, and it can be difficult to collect data in an unforgiving environment. But for every difficult sampling day I encounter, it’s exciting to know the data I collect could be used to develop fisheries management solutions for many years to come.
