- Volume 4, Issue 1, Fall 2002 -
Porpoises in 2002
Data Collected From Porpoises This Year
What Happened in 2001?
Other Weir Visitors
The Mammal Seine
Porpoises Make the News!
Thanks to our Supporters for 2002
And in the winter…
This has once again been a successful year for the Harbour Porpoise Release Program. We would like to thank all of you for ensuring our continued success during 2002, our 12th season.
Here is our annual end-of-season newsletter, telling you about how many porpoises we released, and some of our scientific activities, for the 2002 season.
This year we released 31 porpoises from the weirs around Grand Manan, representing roughly 12% of the number of animals we seined last year. There were a total of 53 porpoises recorded in Grand Manan weirs, with the vast majority of these turning up in Flagg’s Cove. Of the 53, 15 swam out [or left when the twine was taken down], 31 were seined or swept out alive, 3 died during seining, and the fates of 4 animals are unknown. This gives us a seining success rate of 31/34, or just above 91%, for 2002.
Our overall average for the past 11 years is about 94%, so we are close to that this year. We seined for porpoises a total of 24 times in 2002: 8 times with a weir seine, 13 times with the green mammal seine, and 3 times with the new black one. Porpoises swam into weirs all summer: we recorded entrapments from June 9th to the time of the printing of this newsletter (Sept 28th). As in most years, the majority of the entrapments (30) occurred in August, with 5 in June, 7 in July, and 11 in September.
Of the 31 animals we released this year, we were able to collect biological data from 30 (one animal was swept out and thus we weren’t able to learn anything about it). Sixteen of the animals were male, and 14 were female. We had five calves (born this May), 7 juveniles, and 18 adults.
This year’s largest (163
cm female) and smallest (her calf: an 86 cm male) porpoises were both seined
out on July 2 from Intruder. The 30 animals we handled all had uniquely
numbered plastic tags attached to their dorsal fins before they were released.
Tags for males are placed high on the fin, and female tags are positioned
at the base of the fin. This year, males tags are orange and females
are green (2001 colours were yellow for males and red for females).
We were able to weigh 16 of the porpoises we released: the heaviest
of these was a female released from Intruder on August 28th that weighed
in at 62 kg (136 lbs).
We use a heart rate monitor (used by professional athletes; seen here on the right) to measure heart rate as a way of learning about physiology and how stressed porpoises are during seining. We use length and girth to provide us with a general idea of the body condition (by this we mean body fat) of the porpoises we handle. It’s good to be fat if you’re a porpoise!
We also collected blood samples from 15 porpoise this year. These samples are used as part of a long-term study monitoring the health of this population. Blood samples also allow us to evaluate the health of each individual: red and white blood cell counts are used to look at oxygen delivery and search for signs of infection, enzyme levels provide information about organ function, and hormone levels can be used to assess stress and to determine pregnancy in females. We have not yet sent the 2002 blood to the Ontario Veterinary College for the chemistry analysis.
Last year, we collected blood samples from 57 porpoises. Of the 8 female porpoises that were large enough to be considered mature, progesterone levels in their blood indicated that all of them were pregnant (Mother seen here with a calf).
Health information from Bay of Fundy porpoises is also used by rehabilitation facilities in other parts of the world as a guideline for normal blood values and body weights for wild harbour porpoises. For example, the New England Aquarium has spent the summer rehabilitating a juvenile harbour porpoise that stranded in Massachusetts in May of this year. Now that this porpoise is once again fat and healthy, the NEA plans to release it sometime in the next few weeks.
Usually we are able to deploy several tags each year. These tags allow us to remotely track the movements of porpoises via information transmitted via satellites.
Unfortunately we were only able to get one satellite tag out this year, and this tag failed after only 2 weeks while the porpoise was still in the waters around Grand Manan. Last year we deployed four of these tags. Two of them lasted 2 ½ months, and the other two lasted about 10 months. The long-term deployments revealed that these two animals spent most of last winter in the Grand Manan Channel, which is unusual. Most of the porpoises we have tagged move south into the Gulf of Maine in the fall and early winter. This just demonstrates that each season, and each individual porpoise, are different.
Last year was a record year for the Harbour Porpoise Release Program, with a total of 310 porpoises observed in Grand Manan weirs. Fifty-one of these animals swam out, and a total of 244 porpoises were seined or swept out. Our success rate, even with so many animals, was still impressive: 94.6% of seined porpoises were released alive. We seined for porpoises 102 times last year, sometimes 4 to 6 times a day. Often there would be 3-6, or up to 12-13 porpoises in a weir at once. It was impossible to identify any factors associated with entrapment last year (tide phase, moon brightness, etc) because lots of porpoises swam into weirs every night. None of you could ever recall a year like this, or remembered hearing about one in the past. It certainly seemed to be a very unusual summer.
Given the high numbers of porpoise entrapments during the summer of 2001, we had no idea what to expect for 2002. Our last big year for porpoises was 1993, in which 153 porpoise entrapments were recorded, and we released 113 animals. Entrapment numbers for 1992 and 1994 were 72 and 77 respectively, so we thought that porpoise entrapments might occur in cycles. If so, 2002 would again be a busy year, with perhaps 150 porpoises (half of the 2001 total). Apparently, porpoises are as hard to predict as the herring they feed on. This year we saw 1/6th of the number of porpoises swim into Grand Manan weirs, and handled only 34 individuals (a little over 1/8th the number we seined last year).
Surprisingly, after putting on all those plastic rototags last year (214 of the 244 porpoises had rototags), none of these animals swam into weirs this year. We did see some (like the one shown here) swimming around in the wild, particularly around the Whistle Rip. We have narrowed this tag number down to one of three possibilities (70? ….the last digit is covered by algae!) from 2001.
So what happened in 2001? Last year here seemed to be an overall shift of porpoises inshore. Porpoise entrapments are likely tightly associated with herring distribution. Porpoises are small animals and must stay right on top of their food source. It may be that porpoises target a specific size class of fish that was closer to shore last summer. It is also entirely possible that some other factor was responsible for last year’s high entrapment rates. The bottom line is that we can’t predict what will happen each year, or exactly why porpoises move around in the way that they do. Every year we learn a little bit more about them.
In addition to porpoises, there were a few larger visitors to Grand Manan weirs this year. We recorded one minke whale in July, and four humpback entrapments (two of these may have been the same whale visiting twice) in September. All of these whales were released successfully. All four humpbacks (one is shown below) were juveniles.
Note: After this was written two additional humpbacks were found in herring weirs off Campobello Island, one in October and one in late November. Both got out safely, the former after the netting was removed and the latter after top poles and netting were removed. These are by far the latest occurring entrapments of humpback whales in recent years.
Minke whales are infrequent, but not uncommon to weirs: there are usually 2-3 of these animals in weirs each summer, for a total of at least 26 over the past decade. Humpback whales don’t seem to swim into weirs very often; prior to this year we were aware of only 8 such events. Humpbacks (and fin whales) often came closer to Grand Manan shores at night in past years, but for the last few summers they have not been seen very close to land.
One would assume that like those of porpoises, humpback movements in the Bay are also linked to shifts in herring distribution, but some other factor could also have been responsible for the presence of humpbacks in weirs this year.
After the high demand for the mammal seine last year, a second seine was constructed this winter with funds from DFO through the GMFA. This new net is longer (250’) and deeper (65’) than the green one (210’ x 52’), and the mesh is slightly larger (8” mesh, rather than the 4” of the green seine). So far this new black net has been used five times: three times to seine out porpoises and also for sweeping out two humpbacks. These large mesh seines are very effective ways to remove porpoises (and other unwanted animals) from weirs without affecting the herring.
Use of these seines also results in a significant reduction in porpoise mortality. All 3 porpoises that died during seining this year did so in weir seines; we had no 2002 mortality with the mammal seines. Over the past 10 years, 97.5% of all porpoises seined with mammal seines were released alive. For weir seines, this rate is only 81.6%. In all likelihood a combination of many factors, including the high visibility of the twine, the presence of fewer fish to confuse and disorient the porpoises, and the tendency of extra twine to float at the surface rather than create bags and folds at depth, results in a higher percentage of porpoises being released alive with the mammal seines.
We had a film crew from the Discovery Channel visit for several days in August, filming a documentary about the Release Program. The crew was able to get some great footage of the release of a mother and calf from Cora Bell, and three porpoises from Iron Lady.
This show is scheduled to air as part of a series on wildlife on Discovery Channel Canada sometime between February and May 2003. Also keep your eyes open this winter for an article about Bay of Fundy porpoises and herring in an upcoming issue of the National Geographic [Feb 2003].
Harbour porpoises also made the local news on the Digby shore. The Berwick Register ran a story about two porpoises that swam into a weir in Morden, NS on August 24. David Hamilton was able to release the animals without any trouble, saying that the porpoises “were actually very cooperative”. Apparently porpoise entrapments are not common in the weirs around Digby, as these were the first Mr. Hamilton had ever encountered.
Each year the Harbour Porpoise Release Program requires funds for boat gas, seining costs, boat and seining equipment, and to provide room and board and travel costs for the release staff. In 2002 we received support from Connors’ Brothers, Whale and Dolphin Conservation Society U.K., the International Fund for Animal Welfare, and a grant from The Government of Canada Habitat Stewardship Program for Species at Risk. We also receive support from private individuals. It would not be possible to run the Harbour Porpoise Release Program without this generous support, and we acknowledge it gratefully.
During the winter we are scattered all over. Laurie Murison lives on Grand Manan year-round and she can address any questions or correspondence sent to the Research Station. Andrew Westgate is a Ph.D. student at Duke University in North Carolina, working on the population structure of common dolphins in the Western North Atlantic. Sarah Wong has just started an M.Sc. project on macaques at the University of Alberta in Calgary, and will spend several months studying these animals in Ghana next summer. Rob Ronconi has also moved out to Calgary and is making plans to start a graduate project on seabirds. Aleksija Neimanis is working as a veterinarian at a clinic in Toronto. Heather Koopman is a postdoctoral researcher at Woods Hole Oceanographic Institution on Cape Cod, and spends much of her time working on lipids in a lab at Dalhousie University in Halifax.
Please feel free to contact us any time, if you have questions, or suggestions, or want to see us about something interesting you have seen. You can reach us through the Research Station
the Grand Manan Whale and Seabird Research Station Research Station
About the Gaskin Fellow Program
The Gaskin Fellow Program was initiated by the GMWSRS in 2000, in honour of Dr. David Gaskin and his contributions to conservation and science in the Bay of Fundy. The program provides summer employment for a local high school student conducting research on marine mammals in the Bay of Fundy.
A GOOD WINTER AND WE'LL SEE YOU NEXT SUMMER!
Harbour Porpoise Research: 1997 | 1998
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