Marine fisheries in the United States are managed by a plethora of fisheries agencies. For example, the National Oceanic and Atmospheric Administration (NOAA) manages marine fisheries within the U.S. exclusive economic zone (an area that extends from 3-200 nautical miles, nm, off the U.S. coastline), while individual U.S. states generally manage their own fisheries within 3 nm of their coastlines. NOAA Fisheries also works closely with eight regional fishery management councils, which develop fishery management plans for fisheries in each region.
This management hierarchy is designed to prevent overfishing, rebuild fish stocks and protect, restore, and promote the long-term health and stability of U.S. fisheries. As such, these agencies produce a myriad of management advice based upon a dynamic process of collecting and analyzing a vast array of biological and environmental data. These data are often collected via fisheries-independent surveys, or efforts that are separate from the activity of the fishing sector (e.g., data collected by scientists who are conducting at-sea surveys).
In most cases, the primary function of a fisheries-independent survey is to provide an index of relative abundance, or an estimate of fish population size across time. These data are often incorporated into stock assessments to evaluate a fish stock’s health. Scientists employ a variety of fishing gears (e.g., nets, hooks) to collect these data. Different gears catch different species and different sizes of fishes, and the gear(s) scientists ultimately choose to use is/are often dictated by characteristics of the sampling area, such as depth.
When possible, using several fishing gears allows scientists to study fish at varying life stages and habitats to obtain a comprehensive understanding of a fishery’s status.
In 2006, a fisheries-independent bottom longline survey was initiated off the coasts of Mississippi and Alabama by scientists at the University of South Alabama’s Fisheries Ecology Lab to study the larger (and older) fishes in and around Alabama’s Artificial Reef Zone. A bottom longline samples fishes living near the seafloor and is comprised of a weighted mainline, with each end of the mainline marked by high-flyer buoys.
A series of gangions (baited hooks) are attached to the mainline at consistent intervals and soaked for 60 minutes. Upon haul back, fishes that are caught are identified, weighed and measured; once this information is recorded, most fishes are tagged and released.
Since its inception, this bottom longline survey has produced an abundance of data, which has been analyzed to define red snapper and shark distributions and examine the movement ecology of highly mobile apex predators, such as tiger sharks, scalloped hammerheads and great hammerheads. Today, this bottom longline survey is implemented by marine fisheries specialists with the Mississippi-Alabama Sea Grant Consortium and Mississippi State University’s Marine Fisheries Ecology Program in partnership with the University of South Alabama’s Fisheries Ecology Lab.
Despite the importance of fisheries-independent surveys (like this bottom longline survey), the longevity and spatial extent of these efforts are often hindered by challenges in maintaining and implementing these surveys. For example, planning and completing surveys is often logistically and physically demanding, as well as time consuming. Sampling gear, vessel use and personnel are costly, and funding is limited. As a result, sampling opportunities become more restricted while the demand for an ever-increasing scope of information grows, particularly as marine environments withstand anthropogenic change.
To meet these increasing demands, many fisheries-independent surveys incorporate a value-added sampling approach, where sampling protocols are multidisciplinary to maintain efficiency while maximizing the amount of data collected. For example, most fisheries-independent surveys count, weigh and measure fishes that are caught. However, a value-added sampling approach may also involve recording environmental conditions or examining specific body structures (otoliths, dorsal spines, reproductive organs) or tissues (fin clips, muscle, blood) to aid in age determination, maturity status or diet composition of rare or ecologically important fishes.
This extra effort provides substantial increases in data but also consumes precious time on the water. To further streamline sampling efficiency, marine fisheries specialists also implement species prioritization protocols, or procedures that outline different sampling methods for different species. While data-limited species (species for which we have little to no knowledge of stock size or fishery characteristics) may benefit from a full sampling workup, others likely don’t require a similar level of effort.
The incorporation of value-added sampling into our long-term bottom longline survey has provided invaluable data for a multitude of fish life history and ecology studies. For example, these data have allowed us to describe the age and growth of red snapper and red drum, information that is crucial to sustainably managing these fisheries.
The trophic ecology (the feeding patterns and feeding relationships between species within an ecosystem) of Atlantic sharpnose sharks and tiger sharks has also been examined, leading to a more comprehensive understanding of the trophic roles of sharks in the Gulf and the impacts of environmental changes on these predator-prey relationships.
In addition, this bottom longline survey has allowed us to predict suitable habitat for a variety of sharks, thus elucidating differences in habitat use by different shark species and by different sexes of the same species. Current species prioritization efforts are focused on updating age and growth information for tiger sharks and blacknose sharks in the Gulf. The volume of information gained from this long-term survey – and the incorporation of value-added sampling – underscores the importance of maintaining and prioritizing these efforts in years to come.