One Fish, Two Fish
“Counting fish is just like counting trees — except that they are invisible and keep moving,” John Sheperd, University of South Hampton
How do you count what you cannot see? This problem is of particular concern to fishery stock assessment, the collection and evaluation of data to determine the biological parameters of a fishery. Using basic biological descriptors such as growth rate, population size, and natural mortality, fishery scientists can quantify the impacts of different levels of fishing effort in terms of population sustainability and structure. Fishery managers use the results of these models to help make management decisions, with political and economic factors also taken into account.
In order to learn more about stock assessment, I spent a snowy Valentine’s Day traveling from Montreal, Quebec to Rutgers University’s marine field station in Tuckerton, New Jersey for a two day stock assessment crash course. My adviser suggested I come down to learn more about population models and stock assessment since I am currently writing the code (statistical modeling language) for Follensby Pond’s lake trout population, part of my M.Sc. thesis project at McGill University.
Still enjoying Quebec’s frosty winter, but looking forward to summer, warmth, and sunshine – oh how I miss southern California.
The class was a two day modeling blur, punctuated by frequent snack breaks and good company. I learned about age structured models, the pros and cons of modeling in R vs. AD Model Builder (turns out that R is user friendly compared to other programs – who knew!), and of course, how to count fish you cannot see. As it turns out, there are a few options for counting invisible fish including hydroacoustic surveys (using sonar to “see” fish in the water column), capture mark recapture analysis (tagging and retagging fish to estimate population size), and catch per unit effort, the most common for established marine fisheries. Catch per unit effort is exactly what it sounds like: the amount of fish caught (usually biomass in kilograms) per some amount of fishing effort (number of trawls, angling hours, etc).
In the early days of fishery management, scientists would use a curve of catch per unit effort to determine the maximum sustainable yield (MSY), the point of maximum catch that can be sustained for an infinite amount of time. MSY forms the apex of the catch curve and catch beyond MSY results in less catch per unit of effort. By graphing real data of fishery catch, one can usually determine the apex of the curve over time, but not until the fishery has passed the MSY. By this time fisherman are working longer hours and catching less fish, meaning earning less money. While easily said, it is almost politically impossible to reduce fisherman effort to return to MSY. This method of fishery management is based on surplus production models and is rarely used today since it has historically led to fishery collapse.
Watching preparations for a dog sled run on a frozen lake at a resort in the Laurentides (home to this year’s GRIL conference).
After the stock assessment crash course, I spent another two days working on my population model at Rutgers University before returning to Montreal… and left the next day for my first academic conference at a beautiful resort in the Laurentides region of Quebec. The conference was hosted by the Group for Interuniversity Research in Limnology and Aquatic Environments (GRIL) and consisted of academic talks, student bonding activities (limnology games), a poster session, and several delicious all-you-can-eat, gourmet meals. Note: grad students never pass up free food. Although I packed heels, pencil skirts, and fancy blouses, the dress code was more geared towards blue jeans and hiking boots. Is this the norm, or a more conference-specific occurrence? I still don’t know, but I was happy to be wearing hiking boots after frozen rain encased everything outside in a quarter inch of ice.
Pine tree following hours of frozen rain at the GRIL conference.
The resort was beautiful and I had a great time meeting other people from similar fields, but the majority of academic talks were in French. Yikes. Although the PowerPoint slides were often in English, I certainly missed the finer points of most talks, and felt a bit baffled when the entire room would break into laughter from a joke I obviously did not understand.
Presenting the initial results of my lake trout research at the GRIL conference poster presentation.
Another thing that baffled me was the rescheduling of presentations around the Canada-US Olympic hockey game! Only in Canada eh? Next month I will travel to Hawaii on vacation for some much needed sun, fine-tune the population model code for Follensby Pond, and plan the field work logistics for my next bout of sampling. Oh yeah, I forgot to mention that my amphibian paper (undergraduate thesis) was finally accepted for publication. There are still a few edits left before this final resubmission, but I am pretty stoked. More on that soon!