Research Document 1997/21
Status of Atlantic salmon on Prince Edward Island in 1996
By D.K. Cairns
Abstract
Salmon, historically abundant in Prince Edward Island, were eliminated from most streams following European colonization. Since the mid-1980s enhancement and stocking efforts have re-established salmon runs, primarily of hatchery-reared fish, on several PEI rivers. Conservation requirements, developed for rivers with natural salmon runs, are calculated as the spawning escapement that produces 2.4 eggs m-2 of river area. On this basis conservation requirements are 537 large salmon and 288 small salmon for the five most important salmon streams on PEI, including 159 large salmon and 85 small salmon for the Morell, which is PEI's most important salmon stream.
Salmon stocking on PEI relies chiefly on fish that are reared in semi-natural open impoundments and released as 2+ smolts. An estimated 42,691 juvenile salmon were released into the Morell in spring 1996, based on a presumed 65% survival rate of 1+ parr placed in the pond in June 1995.
A licence stub survey estimated that anglers harvested 534 small salmon from PEI in 1996 during 6,478 rod-days. Estimates for the Morell were 397 retained small salmon and 4,156 rod-days. An additional 17 small salmon were taken by native harvesters in the Morell.
Counts of salmon ascending the fishway to Leards Pond totalled 249, of which 60 were removed from broodstock. Sample composition was 88% small (<63 cm fork length) and 86% hatchery in origin. A mark-recapture experiment was conducted at Leards pond and at Mooneys Pond to determine the capture efficiency of the Leards counting facility. Thirty-four of 103 fish captured at Mooneys has been marked at Leards. The median Bayesian estimate of fish entering Leards Pond, adjusted for late running fish which did not ascend to Mooneys, was 563 fish. Counters enumerated 438 salmon redds on the Morell in 1996, of which 308 were above Leards Pond.
Counts at the Valleyfield River fence totalled 75 small and eight large salmon, the largest run in the time series.
Length distributions of juvenile salmon taken during electrofishing surveys were tri-modal, suggesting the presence of 0+, 1+, and 2+ age groups. River-wide juvenile populations, based on 14 electrofishing surveys in August-September and partitioned by age according to length distributions, were 24,312 0+ fish, 7,885 1+ fish, and 9,411 2+ fish.
The return rate of Atlantic salmon stocked above Leards, calculated from the mark-recapture estimate of arrivals to Leards, was 6%. However, this return rate contains substantial uncertainty because the number of fish released in 1995 is not reliably known.
The total 1996 Morell run can be calculated from the 1995 run as estimated by a mark-recapture experiment, assuming a constant efficiency of the Leards trap and a constant distribution of ascending fish to Leards and other destinations. The 1996 run estimated in this fashion 1,920 fish. Exploitation rate based on the stub survey and this estimate was 23.5%.
Salmon entering Leards Pond, corrected for trap efficiency but not adjusted for angler mortality, had a potential spawning deposition of 435,406 eggs in 1996. This represents 243% of calculated conservation requirement. For the Morell as a whole, an estimated post-fishery spawning escapement of 1,523 fish produced 1,537,225 eggs, which is 270% of conservation requirement. Not other rivers on PEI have come close to achieving conservation requirements in recent years.
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