Japanese scientists have fresh insights to conserve the Hokkai shrimp stock

Hokkaido is running a little low on their famous Hokkai shrimp. Hokkaido, a region in Northern Japan, has been known to be teeming with the shrimp which is a popular delicacy. Not only are the Hokkai shrimp known for their distinct flavor, but the traditional sailboats that catch the shrimp are a tourist attraction off the Notsuke Peninsula.

However, the population of the Hokkai shrimp Pandalus latirostris has been declining over the past years. While regulations such as mesh size requirements are in place, they don’t seem to be working as well to maintain the shrimp population.

Dr. Sayaka Ito, Deputy Chief of SEAFDEC/AQD, partnered with scientists from the Japan Fisheries Research and Education Agency (FRA) to study the shrimp in Akkeshi Bay and Lake Akkeshi in Hokkaido. These bay and lake are major fishing grounds of Hokkai Shrimp. Dr. Ito and his team wanted to see how the shrimp’s peculiar growth pattern and somewhat migratory behavior affect Hokkaido’s catch for the season. Let’s showcase some of their findings.

Let’s start with the shrimp’s development. P. latirostris are protandric. That means that they start off their lives as males and, after mating, eventually transform into females. This fascinating aspect of their development ought to be taken into consideration in making fishing regulations for this shrimp. For example, one common population control regulation is by enlarging the mesh size of traps; only capturing the mature shrimp that have finished mating so that the younger ones can still grow and reproduce. However, this may have a negative effect on the shrimp population because all the mature shrimp are female. This would leave the lake with disproportionately more male shrimp than female shrimp.

Then, there’s the matter of the shrimp’s habitat. In Akkeshi Bay and Lake Akkeshi, P. latirostris live in patches of seagrass and seaweed beds and travel among the patches in the lake and bay depending on their growth. As Dr. Ito and his team conducted monitoring on the physical environments of these patches, they found that water temperature and salinity were different among the beds scattered across the bay and lake. In particular, higher water temperature and lower salinity near and in the lake created large patches of eelgrass beds.

Most notably, the egg-bearing females would migrate to the eelgrass beds near and in the lake where it’s less salty and warmer. This is probably because conditions there would help survival of their hatched offspring through abundant food in the eel grass bed and a more rapid molting cycle induced by the higher temperature. This means that if the fishermen want to preserve their shrimp population, they also have to preserve the diverse sea grass and seaweed beds scattered across the bay and lake.

The results of Dr. Ito’s study could provide some insight in sustainable shrimp stock management and greatly help the recovery of the declining shrimp population in Hokkaido.

If you want to know more about the ontogenetic migratory pattern of P. latirostris, in Akkeshi Bay and Lake Akkeshi, and sustainable shrimp stock management, you can read more from the article published in the Journal of Regional Studies in Marine Science entitled “Distribution pattern and habitat use of the protandrous shrimp Pandalus latirostris in relation to environmental characteristics in Akkeshi waters on the pacific coast of eastern Hokkaido, Japan.”

You may request for a copy here: https://repository.seafdec.org.ph/handle/10862/6503.