By Cindy Baker
Lamprey and hagfish (known as cyclostomes or agnathans) are the only living jawless vertebrates. Over 360 million years old, lampreys swam past herds of drinking dinosaurs, and have survived at least four mass extinctions. The brain of the lamprey is believed to be the closest example of our primal vertebrate ancestors, and lampreys provide important insight into the evolution of fins, jaws and the skeleton, plus vertebrate motor control, and immunology.
Lamprey have evolved to utilise the same lifestyle as salmon, freely moving between marine and freshwater environments – and being successful in both. A key difference from salmon is the metamorphosis between life-stages. The larvae (termed ammocoetes) live in the sediments of their natal stream filter-feeding on benthic algae, microbes and other organic material. They have no teeth and are blind. After 3 to 4 years, the ammocoetes metamorphose into a macropthalmia, which migrate to the ocean (or lake) and feed parasitically on the blood and flesh of fish and marine mammals. Akin to a vampire, lamprey have the reputation for being ugly bloodsuckers. They attach to their host using a ‘sucker’ containing a myriad of teeth and bore through the flesh with their raspy tongue. Like mosquitoes, lampreys secrete an anticoagulant that keeps blood flowing. After 3 to 4 years living like an ocean vampire, lamprey cease feeding and return from the ocean between autumn and spring to freshwater rivers and streams to breed and die.
This parasitic stage only occurs in some lamprey species, which includes the sole New Zealand species Geotria australis (also known by Māori as kanakana and piharau). Lamprey are an important taonga species for Māori, and are a prized delicacy for many Māori communities. It is during their freshwater migration as adults that lamprey are harvested by Māori. Lamprey were once prolific, but now believed to be in decline and are rarely seen – especially in the North Island.
Even though lamprey are an important customary fishery, very little is known about their biology, especially with regard to stream and habitat selection during their spawning migrations, and the nest sites of adult lamprey. Recent research carried out by NIWA has shed some light on these knowledge gaps, which will help us protect future lamprey populations.
New Zealand lamprey are unique as reproductive adults. Once adults enter freshwater they will spend up to 16 months becoming sexually mature. During this extensive period in freshwater they don’t feed at all. Most other lamprey species will spawn within 6 to 8 weeks of entering their breeding streams. With the exception of New Zealand lamprey, all other species are known to dig out a nest in stony riverbeds (akin to salmonid ‘redds’), deposit their eggs and quickly die. In contrast, New Zealand lamprey form monogamous pairs underneath large boulders, where eggs are attached in an adhesive clump to the underside of the boulder. Although the female dies soon after spawning, the male remains to guard the nest until all larvae have hatched. Within the Banks Peninsula survey stream, this took seven weeks. This is the first evidence of paternal guarding in any lamprey species.
Further work is focusing on identifying the cue used by adult lamprey to select spawning streams. Research carried out on Northern Hemisphere sea lamprey (Petromyzon marinus) has found adults will select spawning streams using pheromone cues (chemical signals that message other members of their species) released by upstream resident larvae. This investigation is still on-going, but initial results indicate that New Zealand lamprey are selecting spawning streams using the same pheromone cues as the Northern Hemisphere sea lamprey. This suggests that the production of these compounds has not been altered through the course of millions of years of evolution.
Dr Cindy Baker is an Aquatic Ecologist at NIWA.