WHAT'S NEXT FOR SHORTFIN MAKOS?

 

There is now a complete ban on harvesting shortfin makos across the North Atlantic basin.

The International Commission for the Conservation of Atlantic Tunas adopted such ban last November.  Here in the United States, the National Marine Fisheries Service prohibited possession of the species in federal waters as of July 5, and the Atlantic States Marine Fisheries Commission’s Coastal Sharks Management Board agreed that, once the federal ban was put in place, all Atlantic Coast states would be required to adopt a complimentary ban in state waters as soon as the possibly could.  Most, if not all, such states have now done so.

Thus, the framework for rebuilding the shortfin mako stock is more-or-less in place, even if it took a little too long to get it done.  I’m constantly reminded of the costs of delay every time I head out on a shark fishing trip; historically, I’ve caught my first mako sometime around the third week in June, but this year, we’re already in September and I have yet to have even one take the bait.

On the other hand, I’ve had two white sharks in the slick so far this season; one was caught, one very small one clipped a few baits and disappeared into the depths.  When you’ve seen more white sharks than makos enter your slick over the course of the year, the time for very meaningful management measures has certainly come.

But just what comes next for the swiftest shark in the sea?

Last fall's ICCAT action allows for renewed mako harvest beginning in 2023, provided that discard mortality in the entire North Atlantic longline fleet falls below 250 metric tons (about 550,000 pounds). 

Reducing mortality that far doesn’t seem to be a realistic possibility.  However, we can never forget that, except for those few boats that carry fishery observers, there is no way to ground-truth fishermen’s reports of dead discards.  And given that any renewed harvest would probably be limited to those makos that are caught on pelagic longlines and already dead when brought to the boat, there is some real incentive for longline fishermen to underreport discards in the hope of turning such discards into landings.

There is some evidence of false reporting a few years ago, after ICCAT prohibited the retention of makos that could be released alive, but permitted pelagic longline vessels to keep shortfin makos that were dead when brought to the boat.  According to an article in Canadian Geographic,

“Using an at-sea observer program, researchers looked at the scope of animals that were recorded as dead at-vessel to understand the proportions of dead vs. alive sharks.  [Heather] Bowlby [the research lead at the Canadian Atlantic Shark Research Laboratory] says that between 2010 and 2017, 20 to 30 per cent of sharks were reported to be dead once at-vessel.  After the first year of the landing ban, this number jumped to half and then to just under 70 per cent the following year.  She says that the assumption that sharks were being recorded incorrectly could be inferred by the very notable increase of sharks that were now being reported as dead.”

Longliners could easily begin underreporting dead discards once again if such action proved profitable.

But right now, there is no promise of profit for longliners when they catch shortfin makos; under the current rules, the fishermen only incur expense.  As the same Canadian Geographic article observed,

“’Although not directly the target of the ban, people could still derive value from them in terms of being able to sell them,’ says Bowlby.  She explains that, now that sharks can’t be landed at all, it can cost fishermen money when sharks need to be cut off gear.  Hooks and lines can also be wasted.

“’There’s actually a very slight negative incentive to catch these animals, which we’re hoping will actually lead to spatial-temporal management for the fleet,’ Bowlby says.  ‘If they’re catching a lot of sharks, it’s very likely they’ll move to another area so that they’re not both wasting their time or losing gear.’”

Assuming that everyone does, for the most part, play by the rules, how will scientists be able to gauge the future health of the shortfin mako stock?

In that past, that was difficult, but a new genetic technique promises to provide better information.

The technique involves something called “Close-Kin Mark Recapture.”  As described by the Lenfest Oceans Program,

“…the ‘tag’ is not a physical mark, but rather the kinship of sampled individuals.

“Each animal genetically ‘tags’ its two parents at birth.  By collecting tissue samples from a large number of animals (including sharks that have been harvested) and genetically comparing the samples, the researchers can analyze how often such tags are found.  The tags can identify parent-offspring pairs of sharks or more indirect relatedness such as a half-sibling pairs [sic], when the two animals have ‘tagged’ the same mother or father.  Intuitively, the bigger the adult population, the rarer it will be to find tags.

“Just like with conventional tagging, the number of pairs found can be analyzed statistically to estimate the same parameters that managers expect from stock assessments:  abundance, trend, and mortality rate.  The method can also be used to infer populations structure—if, for example, related individuals are located closer to one another than randomly chosen pairs, or if geographic boundaries are identified that related individuals hardly ever cross.”

Biologists supported by Lenfest believe that close-kin mark recapture, which has already been used to inform the management of southern bluefin tuna and some other shark species, will prove valuable to shortfin mako management efforts.  Right now, they are engaged in a feasibility study that, among other things, will seek to determine the geographic scope, number, and sources (with respect to age, sex, size, etc.) needed to produce a reliable population estimate, while also keeping the cost of the population assessment within acceptable levels.

In the end, what comes next for shortfin makos will likely determine whether the population can rebuild.

If fishermen comply with current management measures, if managers are provided with accurate estimates of discard mortality, if fishermen make an effort to avoid setting their gear in areas where makos abound, and if scientists can develop new and more precise means of assessing the shortfin mako stock, that stock has a better than even chance of being rebuilt over the next 50 years.

But if one or more of those things don’t happen—if illegal landings take place, if fishermen intentionally understate their dead discards or continue to fish in areas where high levels of discards are likely to occur, and/or if scientists lack the ability to accurately assess the stock, then the shortfin mako’s chances of rebuilding make a sharp downward turn.

Right now, things appear to be on track.  It would be nice if they stayed that way.