Striped bass have long been a central part of the Commonwealth’s fisheries and remain an immensely popular target of anglers whether they prefer a boulder beach lit by the moon, trolling umbrella rigs along a reef, or casting flies and tossing artificials into a frenzied blitz. This long-sustained passion for striped bass is also an important part of the coastal economy, with rough estimates of $600 million dollars being spent annually by anglers pursuing stripers in Massachusetts alone. Striped bass have also been the focus of several recent management actions following a sustained period of poor spawning success in the Chesapeake Bay, which has historically contributed the majority of stripers to the coastal stock. These are the migratory bass that Massachusetts residents eagerly await to arrive as the spring days grow longer and the water warms…and then mourn in the late fall as the days once again grow short and the water cools. This annual pattern of presence and absence, celebration and dreaming, is a product of the striper’s migratory behaviors.
As most anglers know, striped bass are an anadromous fish, meaning they spawn during spring in coastal rivers, but spend the remainder of the year in estuaries and coastal waters. Individual bass will remain largely faithful to the same spawning river over the course of their lives. Currently, most striped bass are thought to originate in the rivers that feed the Chesapeake Bay, with significant contributions also coming from spawning in the Delaware River, Hudson River, and the rivers feeding Albemarle Sound in North Carolina. However, fisheries managers currently lack an effective way to accurately and quickly identify how much of the striper catch in coastal waters comes from each spawning population. Furthering the difficulty of this task, in each of these spawning populations, it appears that some fish can remain in local waters for most or all of their lives while others favor roaming the East Coast from North Carolina to Maine. These different groups of fish within each population are what fish biologists call “contingents”, and they add another layer of complexity to understanding population fluctuations and how that affects fishing on our shores. This issue has always been pertinent to management of striped bass, but as the amount of spawning fish has declined coast-wide these questions have become a central focus for the future of the fishery, with an eye toward maintaining opportunity for Massachusetts anglers.
During the summers of 2015 and 2016, DMF biologists tagged 260 striped bass in coastal waters of Massachusetts. Tagging was focused in three areas: Boston Harbor, the back side of Cape Cod, and Buzzards Bay/Vineyard Sound. Staff also spread tags out among size classes, focusing on fish below 28” that could not be kept, fish between 28” and 35” that could be kept recreationally, and fish 35” and up that were available to both recreational and commercial fishers (under the regulations at that time). These tags emit uniquely coded acoustic pulses that can be heard by hydrophone receivers up to a kilometer away. DMF maintains an array of more than 100 hydrophones to detect their movements within Massachusetts waters, and because the technology is widely used by researchers along the coast we are able to follow their movements along their entire migratory route. The tag’s 7-year lifespan meant the same fish could be followed over several consecutive years as well. With this strategy, we hoped to describe the fidelity to summer feeding areas, residence times, migratory routes, and spawning groups.
One caveat to the broad hydrophone coverage along the coast is that it can often take a year or more to receive all the data related to tags from other researchers. We have only recently received all the data for bass tagged in this project and a full analysis of the data is currently underway. However, we have been able to make a few important conclusions based purely on data from Massachusetts receivers.
First, stripers in Massachusetts showed remarkable fidelity to broader areas of coastal Massachusetts as 90% of tagged bass detected for four or more years returned to the same coastal area each year. Second, there appears to be little difference in spawning population composition among tagging areas. Most fish returned to the Hudson to spawn, followed by the Chesapeake, and then a very small contribution from the Delaware River (importantly, there was size difference as fish larger than 35” were most often from the Chesapeake). Finally, the migratory route striped bass follow likely affects their mortality in Massachusetts waters because fish that summered north of Cape Cod used the Cape Cod Canal almost exclusively in both spring and fall, which appeared to lead to higher catch rates.
From 2015 until 2020, DMF supplemented the acoustic telemetry work by collecting thousands of genetic samples from fish caught in both recreational and commercial fisheries throughout coastal Massachusetts. By partnering with researchers at University of Massachusetts, University of New Brunswick, and University of Montana, a new baseline was developed for striped bass from North Carolina through the Canadian Maritimes using powerful modern genomic techniques; this can be thought of as a catalog of genetic signatures for different spawning populations. This work was published last year (LeBlanc et al. 2020) and will provide the blueprint for future genetic work in Massachusetts and elsewhere.
By combining the samples collected from thousands of Massachusetts bass with the new baseline, DMF biologists can compare the spawning composition of tagged fish (which we also took samples from) to the actual fish caught by anglers and determine if the behaviors of tagged fish reflect the larger population they were sampled from and if the composition of spawning groups has changed over time. By comparing the genetic signature of tagged fish with their observed movements, we can also shed light on behaviors like straying and range expansion that have been difficult to impossible to get to date. Finally, DMF has recently received funding to develop and test a genetic monitoring program of coastally caught striped bass that would allow managers to differentiate between the spawning populations, rather than treat them as one coastal stock. This would be a pivotal step forward in the interstate management of striped bass.
Over the next three to four years, analyses of acoustic telemetry, genetics, and the two in combination will be ongoing. This work has been supported by recreational permit funds and should pay back that investment with information that will allow DMF to maximize opportunity for striped bass anglers while ensuring that those opportunities are there in future years.
By Ben Gahagan, Biologist