No abstract

We analyzed the movements of Hudson River striped bass Morone saxatilis along the Atlantic coast from the results of a tagging program conducted in the Hudson River estuary between 1984 and 1988. Almost 30.000 striped bass were marked with internal anchor tags; most measured between 200 and 800 mm total length (TL). Interpretations of recoveries are conditional because the distribution and selectivity of fishing effort along the Atlantic coast are unknown. The proportion of total recaptures from outside the Hudson River increased significantly with fish length and by season from spring through autumn. The geographic range of recoveries extended from the Bay of Fundy, Nova Scotia, to Cape Hatteras, North Carolina-a coastal range of about 1,500 km. Most fish recaptured in spring had traveled north and east; recoveries from south of the New York Bight were uncommon until autumn. Many recaptures came from tributaries; far northern recaptures, in particular, tended to occur in rivers or near river mouths. Mean monthly distances between the Hudson River and recapture sites were highest from June through October and increased significantly with fish length. Comparisons with previous studies suggested that the effective coastal range of Hudson River striped bass has expanded since midcentury, especially that of 200-400-mm TL fish. Recapture of a Hudson River-tagged striped bass off Cape Hatteras supports previous winter trawling studies that suggested that large Hudson River striped bass join schools of mixed origin that winter off the mid-Atlantic coast.

From April through June 1991, we tested a full-scale deterrent system for excluding alewives Alosa pseudoharengus from the intake of the James A. FitzPatrick Nuclear Power Plant (JAF), near Oswego, New York. This electronic system produced high-frequency broadband sound (122-128 kHz) at a source level (in decibels [dB] in reference to 1 MPa) of 190 dB. When the system was on, the density of fish near the JAF intake decreased by as much as 96% and the number of alewives impinged on the intake screens at JAF decreased by as much as 87%. The system was effective during both day and night, and its range was greater than 80 m.

We studied the response of the alewife Alosa pseudoharengus to high‐frequency sound to develop an acoustic system for preventing fish from entering power plant intakes. Four groups of alewives were subjected to different frequencies of sounds ranging from 110 to 150 kHz at sound pressure levels (SPLs, given in decibels [dB] in reference to 1 μPa) ranging from 125 to 180 dB. Each group of 20 or 25 fish was tested in a cage that was suspended in a flooded rock quarry. During the day, alewives schooled and strongly avoided pulsed tones (500 ms pulses, 1,000 ms apart) of 110 and 125 kHz at or above 175 dB, a continuous tone of 125 kHz at 172 dB, and pulsed broadband sound between 117 and 133 kHz at or above 157 dB. Although alewives habituated to tones, they avoided pulsed broadband sound at 163 dB more consistently. In one test, alewives did not habituate to this sound after 150 min of repeated exposure, The more consistent response to the broadband sound was probably due to the range of frequencies in this signal. At night, alewives did not school, did not swim actively, and did not react as strongly to the broadband sound. We believe that the diminished avoidance response at night was due to the absence of schooling and to reduced swimming activity.

The retention of two external tags by striped bass Morone saxatilis was determined directly by holding fish in the Hudson River, New York, in 1984 for up to 24 h (absolute retention) and indirectly by examining fish released into the Hudson River and recaptured up to 2 years later (relative retention). The tags were: (1) an anchor tag, placed into the dorsal musculature, and (2) an internal anchor tag, inserted through an incision in the abdominal musculature. The absolute retention of these tag types, and of a dart tag inserted into the dorsal musculature, also was determined by holding striped bass in outdoor pools for up to 180 d. Retention of anchor tags and internal anchor tags was 100% for striped bass held 24 h in the Hudson River. Retention of internal anchor tags (98.0%) was significantly higher than that of anchor tags (42.0%) among fish at large in the Hudson River for 1 year; in the second year, only internal anchor tags were recovered. Striped bass in holding pools retained anchor tags (96%) and internal anchor tags (98%) significantly better than dart tags (50%) during the first 18 d; few of any tag type were lost thereafter. There was no significant difference in mortality among single‐tagged, double‐tagged, and untagged striped bass held for 24 h in the Hudson River and for 18 d in holding pools.