MAIN OBJECTIVES IN 1998
HARBOUR PORPOISE RELEASE PROGRAM
PINGERS AND PORPOISES
MARICULTURE AND PORPOISES
The Harbour Porpoise Release Program was started in 1991 to assist local weir fishermen with the safe removal of porpoises from their weirs. Porpoises swim into weirs during the night but most do not swim out again. While they are inside the weirs they are able to swim, breathe and eat. We work with fishermen and remove the porpoise(s) from the weir in our small boats, allowing the fishermen to harvest their herring catch. We have also developed a protocol that can be used to ensure the safe release of whales using our specially designed marine mammal seine. Fishermen also use this net to remove bluefin tuna and basking sharks from their weirs.
The release program ran from late June to late September. Each day, weather permitting, we monitored all of the weirs on the northern and eastern sides of Grand Manan for the presence of porpoises beginning July 18. The number of entrapped harbour porpoises was higher than in 1997 approaching entrapment figures seen in other years (Table 1). We do not know why the entrapment rate fluctuates from year to year but we assume that it is related to herring densities in near-shore waters. This has increased our awareness of the dynamic nature and complex interactions between porpoises, their environment and their prey, and highlighted the need to consider these issues concurrently.
Table 1: Porpoise weir entrapments
We successfully released (or the porpoises swam out on their own) 31 of 34 porpoises, two died during seining process, and the fate of one was unknown (see Table 2). We collected basic biological data (morphometrics, sex, body mass and blood samples) from 14 porpoises (8 males and 6 females) including the two that died. We also had three minke whales and two right whales (see below) in weirs. All were successfully released. In October a fourth minke whale was trapped in a rather bizarre incident since no netting was on the weir. Presumably this whale swam out on its own.
Table 2: 1998 summary of weir entrapments
A large number of porpoises escaped on their own during 1998. During previous summers typically one or two individuals left weirs on their own. It is unclear what caused this shift but it was a favourable change because it reduced the chance of mortality during the seining process. We spoke to the local weir fishermen about any potential changes to the fishery that might have brought about this change but they where unable to provide any reasonable explanations.
There were 20 operational weirs around Grand Manan during 1998. Nineteen of these weirs were active par-ticipants in the 1998 Harbour Porpoise Release Program. The final weir is run by an individual who has decided not to co-operate with the program. Thankfully his weir is located in an area on the western side of the Grand Manan that is not important porpoise habitat and hence does not get many entrapments. We hope that we can convince this weir owner of the importance of the harbour porpoise program and get his support in the near future. We are encouraged by the fact that we have such strong support from the vast majority of Grand Manan weir fishermen.
Other Porpoise Research
Two porpoises were fitted with satellite tags. One of these devices was a new type of tag designed to transmit both location and depth of dive information. Because the satellite-linked time-depth recorder (SLTDR) required more battery power to transmit the additional dive information, the tag had a short life expectancy of 79 days. The second tag was of the type we have been using for the past 6 years. This transmitter provided location daily and lasted for 115 days. Track data for these two porpoises can be found on the internet at the WhaleNet website.
The data obtained from these tagged porpoises provides a unique insight into how harbour porpoises utilize their habitat in the Bay of Fundy and Gulf of Maine during summer and autumn. We were extremely pleased with the performance of the SLTDR and plan to deploy more of these tags in the summers of 1999 and 2000. We have only just begun to analyse these diving data, but several interesting features have already emerged. For example, the porpoise appeared to exhibit a circadian pattern in her diving behaviour. She made more dives to the depths at which gill nets are set (80-100m) during the day than during the night. These observations are preliminary and will require further analysis and more data before we can draw any conclusions, but the technique is certainly most promising. In addition to data on the depth and duration of dives, the SLTDRs also transmit information on the amount of time porpoises spend at specific depth ranges. These data will be invaluable in assessing the actual risk of entanglement faced by a porpoise by recording the time that an animal spends in the depth range where gill nets are set.
Unfortunately we did not experience similar success with the foraging study. Although we deployed two time-depth recorders on harbour porpoises, we were unable to retrieve any useful data from these tags. The packs had a special magnesium linkage which slowly dissolved in seawater allowing the packs to release from the porpoises after 10-12 hours. They then float at the surface. In one case we could not recover the tag at all, and on the second attempt the tag released itself from the animal after only 30 minutes. This was in sharp contrast to our previous TDR study in which we recovered all nine units we deployed. This lack of success was attributed to a problem in the saddle design. We hope to address these problems and try again in 1999.
This year we initiated a new study aimed at examining the stress associated with weir entrapment and release. There is a great degree of variability in the ways porpoises react to the seining and handling process; some individuals appear to become more stressed than others and this may affect their chance of survival during the seining process. We wanted to identify any factors that could predispose individual porpoises to increased stress, and to recognise indicators of stress during the handling procedure.
In the summer of 1998, we worked with Aleksija Neimanis, to collect preliminary data on the behaviour (reactions and movements) and physiological parameters (heart and respiration rates) of nine porpoises. Aleksija is a student from the Ontario Veterinary College and a former graduate student of the late Dr. Gaskin. We tested various methods of collecting physiological and behavioural data and established a behavioural repertoire for porpoises during handling. We plan to continue this work in 1999. We hope to use this information to improve our handling and release procedures and make them as humane as possible. We believe it is important to attempt to minimise the stress humans impart on wild animals during handling (even when releasing them from traps), and this study represents a means to achieve this goal with porpoises.
Beginning in late May, we began a study to evaluate the potential for porpoises to habituate to "pingers", acoustic deterrent devices currently used on gill nets to reduce harbor porpoise bycatch. From a clifftop, Tara Cox and her assistant tracked porpoises using a theodolite (a surveying instrument) whenever the porpoises approach a mooring she had equipped with a pinger. The closest observed approach of the porpoises to the mooring was measured to determine if there was a change after prolonged exposure to a pinger. We also attached a POD, or acoustic data logger, to monitor echolocation clicks of porpoises to see if porpoises increased or decreased echolocation in the vicinity of a pinger.
We have not analyzed the closest observed approach data yet, but preliminary analysis of the echolocation data indicates that echolocation clicks detected decreased when the pinger was turned on. This could be due to porpoises moving farther away or porpoises falling silent when they hear the pinger. Next summer, we hope to collaborate with DFO and the gill net fishermen to attach PODs to gill nets to determine if the same decrease in echolocation occurs when a pinger is attached to a gill net.
During July we continued our coll-aboration with researchers from the International Marine Mammal Association (IMMA) who are examining environmental disruptions caused by mariculture activities and their effects on local marine mammal behaviour. Anthropogenic noise originating from predator control devices (acoustic harassment devices or AHDs) deployed on salmon farms may have negative effects on coastal marine mammals. The aim of the IMMA study was to determine how the use of AHDs on salmon farms may effect the behaviour and distribution of harbour porpoises.
To accomplish this task, we tracked from a cliff top with a digital theodolite, the number and movements of harbour porpoises around a moored AHD (while both active and inactive). At the same time, the acoustic behaviour of porpoises in the area was recorded with a hydrophone. Although the analysis of data is still underway, there appears to have been a large reduction in the number of porpoises in the study area when the AHD was active. A similar reduction in the level of porpoise vocalizations was found during the active study periods. We hope that this data will be worked up over the winter and published in a refereed journal.
Two harbour porpoises died during a release attempt on August 25th. These deaths were likely caused because many tonnes of herring were in the weir, which caused the porpoises to dive down to the bottom of the net where they were much more likely to get caught. Complete necropsies were performed and samples were taken for life history, diet, genetics, lipid physiology analysis, and structure of locomotive appendages. Since the carcasses were very fresh with a known time of death, samples of blubber, brain, liver and kidney were taken from these animals for NIST (US National Institute of Standards in Technology) as part of a long-term biomonitoring study of animal health.
About the Grand Manan Whale and Seabird Research Station Research Station
The Grand Manan Whale & Seabird Research Station (GMWSRS) is a non-profit research facility located in North Head. The GMWSRS was founded in 1981 by the late Dr. David Gaskin, a professor at the University of Guelph, Ontario and a pioneer of harbour porpoise research on Canada's east coast. Since 1981, the research station has conducted research on harbour porpoises, right whales, seals and seabirds in the Grand Manan Archipelago.
A GOOD WINTER AND WE'LL SEE YOU NEXT SUMMER!
Harbour Porpoise Research: 1997 | 1998
Harbour Porpoise Release Program - home page