Among scientists and non-scientists alike, data are a fundamental component of our lives. Whether we’re managing our bank accounts or hunting down the cheapest gasoline prices, without data, we wouldn’t be able to make sense of our surroundings. Just as epidemiologists use data to study the spread of diseases and meteorologists use data to study weather and climate, fisheries biologists also rely heavily on data – but in this case, the data are used to assess the current status/health of fish populations and predict their future condition.
There are two broad sources of fisheries data:
Fishery-dependent data* are collected directly from the fishing sector – such as commercial fishers, recreational fishers and seafood dealers. These data may be gathered from fisher reporting apps like Tails N’ Scales (in Mississippi) and Snapper Check (in Alabama), fishery observers or phone surveys.
The majority of the data used to assess and predict fish populations are fishery-dependent; however, these data may be subject to biases (i.e. may not paint a complete picture of the fishery). Potential examples include temporal bias (e.g. a fishery may only operate during a specific time of year), geographical bias (e.g. a fishery may only operate in certain areas to maximize catch), size bias (e.g. a fishery may only target the largest individuals of a species) and misreporting.
Fishery-independent data* are collected separately from the activity of the fishing sector, usually by fisheries biologists, in an attempt to avoid the biases inherent to fishery-dependent data. To avoid temporal and geographical biases, fishery-independent projects are generally conducted throughout the year at randomly selected sites within a study area.
To avoid size bias, biologists typically collect data (i.e. fish) using a variety of fishing gears* – tools used to catch fish. Some examples of fishing gears include trawl, gillnet, hook-and-line and purse seine. These fishing gears come in a variety of sizes and are designed to perform in specific parts of the water column (e.g. surface vs. bottom).
For these reasons, different gears typically catch different species of fish – and even when the same species is caught by multiple gears, those gears will typically catch different sizes of that species, allowing fisheries biologists to study multiple life stages of the species.
Take, for example, a plankton purse seine. This gear consists of a net with very small holes in the mesh, set and hauled at the surface of the water. In offshore waters of the Gulf of Mexico, plankton purse seines will collect very small gray triggerfish (Image A) because young of this species prefer to live in surface plankton communities. In contrast, a typical hook-and-line setup near a Gulf of Mexico artificial reef will capture much larger gray triggerfish because these individuals prefer to live near reefs and their mouths are large enough to bite a hook.
Ideally, fishery-dependent and fishery-independent data are used in tandem to obtain the most complete picture of the current and future status of a fishery. So, the next time you land your favorite species and log the capture on your favorite reporting app, know that you’re contributing valuable data for sustainable management of that species into the future.
*The definitions in this blog were adapted from the NOAA Fisheries Glossary, Revised Edition, June 2006.