Tuesday, March 16, 2010

Lampreys of the Deep

Lampreys are pretty cool creatures. They are really old (as a species). They barely even count as a fish since they don’t have bones (they have cartilage) and have a very simple spine (called a notochord). The only fish close to the same age are hagfish, which are also odd looking creatures of the deep ocean. Lamprey have probably been around for the last 360 million years and changed very little in that time!

Even though they have been around for a long time we know much less about their biology and ecology than we do for other fishes. The conventional assumption is that Pacific lampreys use mainstem river habitats (Columbia or Willamette Rivers) mainly as a migration corridor. Adults return from the sea and migrate upriver to tributary streams (much like salmon) to spawn and die. Juveniles migrate downriver to the sea after spending a time period in the tributary streams. In the sea they begin their parasitic part of their life. Nobody really thinks they use the mainstem areas as a place to live – although no one has ever really thoroughly looked.

We used quite a contraption – a deepwater electrofisher – to collect lamprey ammocoetes from deepwater habitat in the Lower Willamette River from Willamette Falls downstream to the confluence with the Columbia River. Ammocoetes are the blind larval stage that burrow into the sediment and filter feed detritus and organic material. Our contraption is basically an electrified suction dredge. The “bell” is lowered to the bottom with a winch and the pump is turned on. Then the electricity is turned on and any ammocoetes that are in the sediments are stunned and sucked up and filtered through a basket. No, we don’t get any other crazy things from the bottom - like bones or sunken treasure. Most of the time we just got little bits of mussel shells and twigs. The video at the bottom shows the device in action.

Sure enough – the lamprey larvae were down there! We found both Pacific lamprey and western brook lamprey (a native non-parasitic freshwater lamprey) in water up to 53 feet deep! We even found them right in downtown Portland. We found them in shallow water and we found them in deep water. At this point we really couldn’t identify a pattern to where they may occur. We also found a wide range in sizes from less than 20 mm to over 140 mm meaning that they are likely a variety of ages. They weren’t really there in high numbers but they were there consistently enough to start thinking that they might be using these habitats to live and grow. Although we are not sure if the larvae migrated there or were “swept” downriver by strong currents it is conceivable that they are using the mainstem sediments as areas to feed and grow. Interestingly we did not find any larvae in the Multnomah Channel even though we thought this may be a good area for them – and we looked at over 60 sample sites! They may be in the channel but probably just in really low numbers.

It is encouraging and exciting to find lamprey in these areas but it also poses a whole host of concerns regarding lamprey welfare. Issues like channel dredging, contaminants, and flow alteration are examples of things that need to be studied further to understand their effect on the larval lamprey. We plan to keep looking in more areas for the lamprey larvae. We are going to look in the Columbia River at various locations downriver toward the estuary. We also want to look below and above some of the mainstem dams like up in Bonneville Pool. Also, it may be interesting to look at areas before and after channel dredging occurs to evaluate the potential impact of this activity. Stay tuned for future lamprey updates.


video

No comments:

Post a Comment