Sunday, January 6, 2013

Right Whales in Weirs

So what is a right whale doing close to shore?  In the calving areas and in Cape Cod Bay, right whales are sometimes were close to shore but we tend not to think about these occurrences and expect them to be well offshore.

In the Bay of Fundy, typically the largest zooplankton masses are concentrated in the deep water of the Grand Manan Basin which is between Grand Manan Island and Nova Scotia.  However, some right whales do wander and come close to shore, particularly in the spring or fall when zooplankton patches have yet to form or are beginning to break apart.

There were at least three documented cases of right whales in herring weirs, passive fish traps, in the Bay of Fundy prior to 2012.  These five whales were all released successfully:
  • 1976 when a mother and calf swam into the Brown's Weir, now called the Mystery Weir, on Grand Manan Island.
  • 1998 when two right whales swam into Bradford's Cove Weir, on Grand Manan Island (the weir operators said that they had another right whale in that weir before but no documentation exists for that occurrence).
  • 2006 when one right whale swam into a weir in Deadman's Harbour on the New Brunswick mainland.
Bradford's Cove herring weir seen from the air in November when the netting has been removed for the winter but the stakes and top poles are left in place.
So it was not totally unexpected when a call came in on August 26 that there was a right whale in Bradford's Cove Weir.  It was reported by people staying at a cottage overlooking the weir in this remote cove on the south western side of Grand Manan Island.  The male right whale #1708, was successfully released after a number of top poles and stakes and the netting on the outside of the weir were removed and the whale safely swam out. In 1998, netting was also dropped and top poles and stakes had to be removed before the two right whales would swim out, one following the other.
Right whale #1708 in Bradford's Cove weir August 26, 2012.  The rough skin patches on the whale's head allow each whale to be identified individually.

Right Whale #1708 in Bradford's Cove weir.  Although right whales lift their tail when diving, their tails often are uniformly black and are not used to identify individual whales.

Right whale #1708 on the day of his release from the Bradford's Cove weir, August 27, 2012.  Fisheries and Oceans, Campobello Whale Rescue Team and the weir operators monitored the whale's condition and worked to remove netting, top poles and stakes to allow the whale to swim out.

We were surprised by a second right whale on October 17, #3790, in Mystery Weir.  The sex of this whale is unknown, although it is suspected to be a female from photos taken of it in the weir.  Mystery Weir is in Whale Cove on the northern end of Grand Manan Island.  The weir operators were going to take the netting down for the winter when the whale swam in and continued with the plan.  As soon as the bottom netting was dropped, the whale squeezed out between the stakes to freedom and no stakes needed to be removed.  The stakes in this weir are more widely spaced than in the Bradford's Cove weir and obviously the whale felt confident pushing its way out.  In 1976, no stakes were removed either and both mother and calf escaped when the top netting was dropped.

Right whale #3790 in Mystery Weir, October 17, 2012.  the top netting had been dropped but the bottom netting was still in place.

It is a bit ironic that the weirs involved in the two entrapments in 2012 have also entrapped right whales in the past, but both weirs are large and actually had netting up, unlike most herring weirs in 2012. Few herring weirs had netting up because of very low herring catches in the last few years.  Also ironic is that right whales do not eat herring but rather zooplankton.  However, zooplankton patches were not large this year in the Bay and the copepods did not have large fat reserves for overwintering.  The right whales may simply have been looking for other food sources.  Mystery Weir netting was completely meshed with skeleton shrimp, Caprella mutica, a species from Japan that was first reported in the Bay of Fundy in 2003.  The odour trail from these crustaceans may have peeked the curiosity of this right whale but in the end, entrapped the whale.
Right whale #3790 before swimming out between the stakes after the netting was dropped.  The whale spent the night in the herring weir before escaping.
If we could be sure that right whales have temper tantrums, then #3790, was certainly exhibiting symptoms.  The exhales could be be heard echoing through the cove and kept people awake during the night it was entrapped.  It definitely wanted out but when it did leave, it worked slowly toward the east, diving regularly and moving back and forth along a tide streak.  Fortunately, the whale was observed on several surfacings after escaping and it was apparent that on its way out of the weir, it made a clean break with no entangling lines or netting.

Right whale #3790 entrapped in a herring weir off Grand Manan Island, October 17, 2012.
With the 2006 entrapment, there was no netting involved, having already been removed for the winter.  However, the wooden stakes were very close together and did not provide any opportunity for the whale to swim out between stakes.  Why don't the whales swim back out the way they came in, through the large opening called the mouth?  Unfortunately, the mouth is often in shallower water, facing the shore and is indented into the trap, creating a pocket (or hook) on either side.  The whales are intent on getting back into deeper water and spend most of their time on the back of the weir which faces deeper water and freedom.  This design is deliberate to keep herring in the trap and does a good job with whales and porpoises as well.

We would like to thank all of those involved from the weir operators, to the people who reported the entrapped whales, to the New England Aquarium for identifying the individual whales to the Marine Animal Response Network for spreading the word amongst the responders and Fisheries and Oceans.

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