Surprising Results

2019-2022

Striped bass stripes can have aberrations, some of which can be used to identify individual fish. Many students have taken pictures of these aberrations to see if fish can be identified from year to year in Eel Pond. In addition, control studies have been run to make sure that the aberrations do not change over time. In 2022, Alanna Hughen and Hannah Birmingham were able to compare fish pictures taken when fish were tagged with pictures they took of the same fish the following year. They were able to identify individual fish by their aberrations indicating that the aberrations did not change year-over-year. These results are similar to identification of whales by fluke patterns. This work is being prepared for publication.

Striped bass have been implanted in Eel Pond, Woods Hole, MA, with acoustic tags in fall 2018, 2019 and 2021. After tagging the fish remain for one to two months and then begin their migration south. Roughly 50-70% of the tagged fish from each cohort return the following spring/summer to Eel Pond. Of the 20 fish tagged in 2021, 14 returned in the spring/summer of 2022.  The attrition continues in sequential years, and we do not expect any of the fish tagged in 2018 or 2019 to return in 2023.  However, we expect around seven or so fish of the 2021 cohort to return in 2023.

What are the causes for attrition in numbers over time?  Some fish are caught and kept. Others are caught and released and may not survive if not handled properly. In addition, some fish that have spent a few summers in Eel Pond have been detected in other locales subsequent summers. That is, a fish that does not return to Eel Pond may have chosen another location.

During the summer 2022, 14 tagged fish that returned were monitored 24/7 by receivers positioned around the pond. By comparing the time for signals emitted from acoustic tags to reach each receiver, it is possible to determine the location of an individual fish every 2-10 minutes. In this way the movement of fish within the pond can be determined. Initial results indicate that the fish are not very mobile during the day but move around the pond in the evening presumably foraging for food. They appear to have a daily movement rhythm, staying in shallow water during the day and moving to deeper water in the evening.

We will continue to monitor fish that return to Eel Pond in 2023.  A separate study will monitor fish movement in relation to anthropogenic sounds in Eel Pond.  A third study will focus on the effects of anesthetic on fish movement.

2016-2018 Results: external tags

Eleven striped bass were tagged in Eel Pond, Woods Hole, MA, with external loop tags and internal PIT tags between 10/5/2016 and 10/12/2016. Three to four of those fish returned the next spring, May, 2017, but only for a week or two. One of the eleven striped bass was caught and released in West Falmouth harbor in October, 2017 by Maks Lunev. A year later (October, 2018) one of the eleven tagged fish was spotted in Eel Pond. Maks, his brother Davide and Steve Zottoli appear in the picture below. These results indicate that striped bass return to Eel Pond. Interestingly the population we tagged returned transiently and only in the Spring and Fall. Did we tag migrating fish that utilize Eel Pond as a temporary feeding and resting place? Make a hypothesis and suggest a way to test it.

2018 Results: acoustic tags

Five striped bass were tagged with acoustic tags in September/October of 2018. All of these fish left Eel Pond, Woods Hole in October. Interestingly only two of the fish left on the same day. A receiver in Long Island Sound picked up a signal from two of the fish. Where are the remaining 3 fish?

Graph when the five fish left Eel pond using data available in the Lesson Plan on Migration. If striped bass are known to school, why did each fish leave Eel Pond separately? What environmental/ internal factor(s) triggered the movement of these fish out of Eel Pond? Where will these fish go and how can we detect their location?