Porpoises in The Mystic
- Hi All,Below is an article written for the Aquarium Magazine by Jim Rice who is a biologist for the NEAQ. Jim should be familiar to a few of you as he gave a talk to the watershed last year and has talked with John Durant. His porpoise project has been funded by Mass. Env. Trust for the last three years but that money has dried up. The EPD Marine Division is going to assist him by making the patrol boat available for the placement of the acoustic sensors. If there is any agency/organization that could help with funding/personell please contact me.This article may be reprinted but only in it's entirety and with the copywrite notation.
Boston Harbor Porpoises
by Jim Rice
Rescue and Rehabilitation Department, New England Aquarium
“You’d better come quick! Some of your dolphins have escaped and are stuck in the Fort Point Channel!” A few minutes later another call comes in; “There’s a lost baby pilot whale swimming next to the Constitution! Can you save it?” Such are the sorts of urgent calls that typically flood our hotline every spring in the Rescue and Rehabilitation Department. Sure enough, most are cases of mistaken identity (for starters, the New England Aquarium hasn’t kept dolphins in its collection for over a decade), but the excitement in the callers’ voices is impossible to miss. And it hardly subsides when we assure them that there’s no reason for alarm, that what they are witnessing is a normal and anticipated rite of spring. Harbor porpoises (Phocoena phocoena) have once again taken up residence in the harbor.
People are often amazed and delighted to suddenly notice a small dark dorsal fin poking through the water as they cross the Summer Street Bridge or take a ferry from Charlestown. These encounters can help us realize the diversity of wildlife at our doorstep, and even promote a whole new appreciation for the harbor. And until fairly recently, sightings of harbor porpoises were uncommon in Boston. But since the early 1990’s, seasonal reports of these small cetaceans (whales) near the city’s waterfront have become a regular occurrence. And many people now view the return of porpoises to Boston Harbor as proof of the harbor’s recovery.
For the past three years I have been studying the use of Boston Harbor by these animals. I was initially driven by the need to find answers to the many pressing questions we hear from concerned citizens: “Is it alright for porpoises to be here? Are they healthy? Can they safely get back out to the ocean?” Over time (and satisfied that the answer to each of these questions was likely YES) I became increasingly interested in the porpoises’ activities, and new questions began occurring to me. What attracts these animals to such a busy, degraded, urban habitat? Which areas do they use most heavily? How do human and porpoise activities overlap? And to what extent do porpoises have a stake in the health of Boston Harbor? In March of 2000, I began a long-term project to document and better understand the use of this urban habitat by these small whales.
My primary objectives with this study have been to estimate the abundance of porpoises in the harbor, and to describe their distribution and activities. Most of this work has involved the use of boat surveys throughout the waters of the Inner Harbor and the Mystic and Chelsea Rivers, aboard been NEAq vessel Dogfish (a 22’ Boston Whaler). Transect runs are typically done two days per week between the months of March and May, with the helpful company of 2-3 volunteers to assist with observations, video/photo documentation, and recording of data.
This year I am also incorporating some new methods and technology to the study. In addition to surveys, I have set several electronic devices at various locations in the harbor in order to continuously “listen” for and record the echolocation clicks of porpoises (the sounds they emit while navigating and searching for food). These units can constantly monitor for porpoises, 24 hours a day and in all weather conditions, so finding relationships between porpoise activity and time of day, tide cycle, and vessel traffic is now possible. I am also hoping to determine what species of fish these animals eat, to better understand how porpoises fit into the ecology of Boston Harbor.
So far, my data suggest that porpoises occupy Boston Harbor, in varying numbers, from early March through May each year, with a peak in mid-April. Sightings have been made throughout the Inner Harbor, including the main channel adjacent to the airport, the mouth of the Charles River, the lower Mystic River and even up into the Chelsea River (which is notorious for high levels of sediment contamination). Many sightings have been made in high traffic areas, and several near-collisions with high-speed vessels have been observed. Porpoises also make short-term use of specific areas within the harbor. They are often present one day and absent the next.
Overall, Boston Harbor appears to be a regular transit point for porpoises at critical periods when the “young of the year” are becoming independent from their mothers, and when the bulk of the Gulf of Maine / Bay of Fundy population is migrating northward (and inshore). Many of the animals sighted during surveys appear quite small, and are presumably young animals. And interestingly, after looking at our historic stranding records, I discovered that the vast majority of stranded porpoises from Boston Harbor (collected since 1969, n=55) have been immature animals. Their average body length is a mere 114 cm, which is significantly smaller than the average lengths of animals stranded in the other regions we study (Maine, New Hampshire, and the remainder of Massachusetts). Animals of this size (at this time of year) can be estimated to be 8-10 months old, around the average age of weaning.
So just what is the significance of Boston Harbor, and perhaps similar urban habitats, to harbor porpoises? I wonder whether estuaries such as Boston Harbor serve as alluring environments for young weaning porpoises learning to hunt for food on their own, perhaps for slow moving prey in relatively shallow water. As a large drainage basin for several river systems (and a staging ground for spawning anadromous fish such as alewives and smelt – presumed porpoise prey) Boston Harbor may represent an important and necessary ecological zone for harbor porpoises at a vulnerable age.
Investigating the role Boston Harbor plays in the life history of these animals is certainly a fascinating task for me. The next time you’re at the waterfront, keep your eyes peeled for those little dorsal fins. There’s a lot happening beneath the surface.
Copywrite New England Aquarium
Reprinted by permissionOfc. Patrick Johnston
Everett Police Marine Unit