New Research on Striper Migrations

Well, I started looking at the Chesapeake Bay newsfeed, and the only one that caught my eye was NOAA announcing Four Fisheries Research Projects to Connect Chesapeake Bay Fish, Changing Habitat, and there, among the four was:

The University of New Hampshire’s project, “Leveraging Multispecies and Multiyear Telemetry Datasets to Identify Seasonal, Ontogenetic, and Interannual Shifts in Habitat Use and Phenology of Chesapeake Bay Fishes,” addresses synthesis and analysis of existing information that connects living resource responses to changing habitat, climate, and other environmental conditions. This project is recommended to receive a two-year total of $249,017.

Huh? What are we going to pay a quarter million for? (That's about one federal research quanta these days, and doesn't really go very far.) Anyway, I googled the title and got nothing, but this came up, a recent article in PLOS One on Striped Bass migration Differential migration in Chesapeake Bay striped bass by David H. Secor, Michael H. P. O’Brien, Benjamin I. Gahagan, J. Carter Watterson, Dewayne A. Fox

Abstract

Differential migration—increased migration propensity with increasing individual size—is common in migratory species. Like other forms of partial migration, it provides spatial buffering against regional differences in habitat quality and sources of mortality. We investigated differential migration and its consequences to survival and reproductive patterns in striped bass, a species with well-known plasticity in migration behaviors.

A size-stratified sample of Potomac River (Chesapeake Bay) Morone saxatilis striped bass was implanted with acoustic transmitters and their subsequent coastal shelf migrations recorded over a 4-yr period by telemetry receivers throughout the Mid-Atlantic Bight and Southern New England. A generalized linear mixed model predicted that ≥ 50% of both males and females depart the Chesapeake Bay at large sizes >80 cm total length. Egressing striped bass exited through both the Chesapeake Bay mouth and Delaware Bay (via the Chesapeake and Delaware Canal), favoring the former. All large fish migrated to Massachusetts shelf waters and in subsequent years repeatedly returned to regions within Massachusetts and Cape Cod Bays. Within this dominant behavior, minority behaviors included straying, skipped spawning, and residency by large individuals (those expected to migrate).

Analysis of the last day of transmission indicated that small resident striped bass experienced nearly 2-fold higher loss rates (70% yr-1) than coastal shelf emigrants (37% yr-1). The study confirmed expectations for a threshold size at emigration and different mortality levels between Chesapeake Bay (resident) and ocean (migratory) population contingents; and supported the central premise of the current assessment and management framework of a two-contingent population: smaller Chesapeake Bay residents and a larger ocean contingent. An improved understanding of differential migration thus affords an opportunity to specify stock assessments according to different population sub-components, and tailor reference points and control rules between regions and fishing stakeholder groups.

80 cm corresponds to about 31.5 inches, about the size that the stripers appear to disappear, this study seems to confirm that. Certainly, strippers bigger that that hang around the Bay in summer.

It also confirms that resident stripers have a far higher mortality than the stripers that leave the Bay and migrate up and down the coast, but doesn't deal with the question of why. Is it fishing pressure (certainly high in the Bay), or disease (also certainly a problem for fish in the Bay)? 

The Wombat has Rule 5 Sunday: Jodie Comer ready and waiting.