Rick Wahle is a marine scientist at the University of Maine, and every year, he quantifies the number of baby lobsters at monitoring sites in Canada and the United States.
His American Lobster Settlement Index (ALSI), published every year since 1989, shows over 100 monitoring sites from New Brunswick to Cape Cod. The monitoring includes two methodologies – diver-based suction sampling and passive post-larval collectors.
Both methods quantify newly settled young-of-year (YoY) and older juvenile lobsters at the end of the larval settlement season between August and October. The latest ALSI report for 2016 has been published.
ABC News is reporting that Wahle says that despite a 10-year trend of high egg production, the index is showing a decline in baby lobster numbers. Scientists and fishermen are working hard to better understand the decline.
A perplexing disconnect between high egg production and low YoY
The ALSI report cites the record-number of early larval stage lobster counts, noting the high count is “what would be expected from the growing numbers of adult lobsters evident both in commercial landings and NOAA trawl surveys.”
But the report says that this is where the “big disconnect” comes in soon after. By the time the eggs reach the post-larval stage, about two weeks later, the growth trend begins to decline. This has been going on since 2007.
The ALSI report cites three possibilities for the decline in baby lobster counts: ” including the possibility of rising numbers of predators, a shrinking food supply, or unfavorable currents as being responsible for the heightening losses of lobster larvae. There is evidence of the decline of zooplankton prey the lobster larvae eat as being a factor.
So, with declining zooplankton and the resulting decline in baby lobsters, the scientists are perplexed. However, a study released by the University of Maine Darling Marine Center and Bigelow Laboratory for Ocean Sciences in September 2016 focused on how larvae of the American lobster will be affected by ocean acidification and warming ocean waters, just two aspects of climate change.
At the time, Wahle, a co-author of the study said, “It’s critical to know how climate change will affect the future of our most important fishery. We only need to look to the die-offs south of Cape Cod to see how climate change is having an impact.:
While the 2016 study was the first published study that focused on lobster larvae, it would be interesting to find out if the decline in zooplankton is a primary factor in the decline in baby lobster numbers, plus, more importantly, what is causing the decline in zooplankton?
