CLIMATE CHANGE IS SHIFTING TIGER SHARK POPULATIONS

CLIMATE CHANGE IS SHIFTING TIGER SHARK POPULATIONS NORTHWARD

A new study has found that tiger sharks’ seasonal distribution has expanded in the northwest Atlantic Ocean over the last several decades. This large-scale northward expansion was driven by climate change, specifically the overall warming of the U.S. Northeast Continental Shelf Large Marine Ecosystem, researchers found. The research was published in the journal Global Change Biology.

“Our tagging and tournament sampling data show that tiger sharks have always spent time in northern latitudes at least going back to the 1960s and 1970s,” said Cami McCandless, study co-author and lead for the NOAA Fisheries’ Apex Predators Program. “But now they are not only arriving earlier but spending more time in northern latitudes due to ocean warming.”

Tiger sharks are a highly migratory species with a distribution that stretches from Cape Cod, Massachusetts to Florida and the Gulf of Mexico. They prefer warm waters (roughly 72 degrees Fahrenheit or warmer). This paper presents empirical evidence of a climate-driven shift in distribution and migration timing for an apex predator—a species at the top of the marine food web. • Satellite telemetry data from the University of Miami • Remotely sensed environmental data from NOAA CoastWatch • Habitat modeling • Capture data (both tagging and recapture events) from the NOAA

Fisheries’ Cooperative Shark Tagging Program

The tagging information was based on data from 47 tracked tiger sharks from 2010–2019, which were detected at 5,776 locations throughout the Atlantic. They compared this data to 8,764 tiger shark capture locations from the tagging program spanning nearly 40 years (1980–2018).

Rapid Northward Expansion Tiger sharks are arriving in northeast shelf waters earlier and expanding their movements north during these migrations when years and seasons experienced high sea-surface temperature anomalies. Satellite telemetry data suggest that, on average, for every 1 degree increase in sea-surface temperature anomalies, tiger sharks have arrived in northern waters 14 days earlier. They also extended their movements farther north by nearly 4 degrees of latitude.

Tiger sharks are not targeted commercially in U.S. waters, but they can be caught as bycatch. Increasing water temperatures have shifted tiger shark movements beyond management areas that are closed to longline activities, increasing their vulnerability to these fisheries. Data from the Cooperative Shark Tagging Program support these findings. They indicate that the northern edge of high-catch density areas shifted north during the warm seasons by more than 400 kilometers since the 1980s. This paralleled a shift in their preferred temperature range (26–28 degrees Celsius, figure below). The capture data also showed progressively earlier tiger shark catches in northern waters across years.

To investigate changes in tiger shark seasonal distribution, the authors used combined analyses of:

Other biological, demographic, and environmental factors may also contribute to these habitat use patterns. However, the authors concluded that climate change is a major force.

Climate Change Impacts on the Northeast Ecosystem

The global ocean has warmed steadily since the 1970s. Some of the highest rates of change are in productive areas such as the U.S. Northeast Continental Shelf Large Marine Ecosystem. Research has documented some climate-driven shifts in distributions for marine species, but these are highly variable among taxonomic groups and ocean regions. Key research priorities are determining the rate and direction of range shifts and understanding the mechanisms driving them.

McCandless said, “This research highlights the importance of continuing long-term data collection programs, like our Cooperative Shark Tagging Program, to help monitor species distributions and migrations as their environment continues to change.” FIGURE 5

Distribution changes affect predator-prey relationships, when and where human-wildlife conflicts occur, and other factors. Research like this, which identifies the effects of climate change on a species, allows resource managers to incorporate distribution changes into management decisions.

Decadal patterns in high catch density areas of tiger sharks and associated decadal averages in seasurface temperatures (SSTs). High catch densities are based on 50% density volume contours from kernel density analysis on 8764 tiger shark captures between 1980 and 2018. SSTs are averaged by decade for both cold seasons (November–April; top row) and warm seasons (May–October; bottom row). Provided for spatial reference, two letter abbreviations for US states are FL = Florida, SC = South Carolina, NC = North Carolina, VA = Virginia, PA = Pennsylvania, NY = New York State. Underlying SSTs are on a gray scale; the vertical arrow in the legend indicates direction of temperature preference from lowest to highest (white to black)

RFA PRIORITIES:

WHAT WE’VE BEEN WORKING ON

Harvest Control Rule: A framework addendum to the Summer Flounder, Scup, Black Sea Bass and Bluefish fishery management plans was recently passed by the the Mid-Atlantic Fishery Management Council (MAFMC), and the Atlantic States Marine Fisheries Commission (ASMFC) that would institute a new approach for setting recreational measures in these fisheries. That approach would take into consideration other elements of the fishery including stock size, recruitment, biological references and stock trends as opposed to relying solely on the estimates produced through MRIP and comparing those estimates to the recreational harvest limit. This outdated approach is responsible for the current reductions in black sea bass and scup even when the stocks are far above their rebuilding target. The Harvest Control Rule may have far reaching applications for other federally managed species. Tip of the hat to longtime RFA Member and MAFMC member Captain Adam Nowalsky for his leadership on this issue.

30/30 Initiative: is an initiative developed by the UN the United Nations Convention for Biological Diversity in 2015. In January 2021, President Biden issued an executive order, seeking to conserve 30% of the nation’s public lands and waters by 2030. RFA contends that the US already has ample protection of its lands and waters and that those areas need to be quantified before proposing any additional areas. We are also making the case that recreational activities, such as fishing must be allowed in those areas. The 30/30 initiative also is sparking interest in pushing for the establishment of new marine sanctuaries and monuments, something RFA is adamantly opposed to. RFA will continue to remain engaged on this issue.

Northeast Groundfish: RFA’s New England Regional Director Capt. Barry Gibson serves as Vice-Chair of the New England Fishery Management Council’s Recreational Advisory Panel (RAP). The RAP has been dealing with recreational measures for Gulf of Maine cod and haddock and was successful in raising the recreational daily bag limit for haddock from 15 to 20 fish per person for 2022, which was also a major victory for the for-hire fleet as this will help increase business. The RAP also was able to get the fall recreational cod season for private boat anglers extended an additional two weeks, to four weeks total, in September, giving anglers extra opportunities to catch and retain cod.

Atlantic Mackerel: Mackerel have been designated as overfished by the Mid-Atlantic Fishery Management Council (MAFMC), and a 50% cutback in recreational catches has been proposed. RFA’s Barry Gibson and RFA Massachusetts Chairman Mike Pierdinock have been working to help mitigate measures and to provide data and angler feedback on mackerel usage as bait by recreational striped bass and tuna fishermen, and to provide information on when and where mackerel spawn. As a result, the MAFMC eliminated consideration of closed recreational seasons and minimum sizes and has approved a bag limit of 20 mackerel per day per person, which is acceptable to most in the recreational sector.

Offshore Wind Farms: RFA’s Barry Gibson and Mike Pierdinock have been very active in addressing the increasing use of offshore waters for wind turbine farms off the New England Coast. Gibson worked with the State of Maine’s Dept. of Marine Resources to move a potential site for a 12-turbine array away from Plattes Bank, an important recreational and commercial groundfish and tuna fishing ground in the Gulf of Maine, to a site farther east where recreational fishermen would not be impacted. Pierdinock has been very active in the siting of wind farms off Massachusetts that could impact recreational fishing grounds and in collecting data that indicates potential negative impacts on fish and other sea life by underwater electrical transmission cables and their resulting electromagnetic fields.