John M. Casselman

Growth and Relative Size of Calcified Structures of Fish

Abstract The relationship between size of calcified structures and the body of fish has been used widely in fisheries science to estimate body size at a younger age by “back-calculation.” I labeled the calcified tissue of northern pike Esox lucius with tetracycline to examine the concurrent linear growth of calcified structures and the body. I also conducted comparisons of the sizes of one or more calcified structures with body sizes of northern pike, lake trout Salvelinus namaycush, and muskellunge Esox masquinongy. Over a broad size and age range (juveniles and older), growth of scales, cleithra, and otoliths is only transitorily isometric in relation to body growth. Although scale growth is more strongly allometric than bone growth, allometry in both structures is positive during rapid growth and negative during slow growth. Slower-growing individuals have relatively smaller scales and cleithra. Calcified structure-body relations indicate that in older fish, growth of the scales virtually ceases while ...

Dynamics of Resources of the American Eel, Anguilla rostrata: Declining Abundance in the 1990s

The American eel (Anguilla rostrat) is a catadromous panmictic species that has long provided important fisheries (Eales 1968). These resources have been heavily utilized across its North American range (Fig. 1). However, from the mid-1980s throughout the 1990s, commercial catches declined dramatically as value and fishing effort increased. This change is confirmed by most scientific indices, especially those that are long term and fishery independent. Indeed, the earliest and best documented index comes from the number of juvenile eels ascending the eel ladder in the St. Lawrence River (Fig. 1) at the Moses Saunders Hydroelectric Dam (Fig. 2) (Castonguay et al. 1994a; Casselman et al. 1997b). As the ladder is an index of recruitment at the extremity of the population range of this panmictic species, Casselman and Marcogliese (2000) and others have contended that it provides evidence of general species decline, reflecting inadequate juvenile recruitment to maintain distant stocks. Decline of the long-valued, highly productive St. Lawrence River-Lake Ontario (SR-LO) stock is of particular concern because it is the largest source of old (1960s, maturing silver phase, range 13-42 years, mean 19.7 ± 1.1 years), uniformly large (915 ± 24 mm, 1902 ± 166 g), fecund spawners. Fecundity is directly related to size (Barbin and McCleave 1997), and Castonguay et al. (1994a) concluded, from the relative size of the watershed, the largest available to the species, that the SR-LO stock could contribute up to 19% of the overall female spawning stock. The decline in this stock’s contribution could cause a major loss of escapement of fecund spawners from the continent, accelerating deteriorating recruitment and species decline and resulting in diminishing overall resources.

Lake Trout Spawning Habitat in the Great Lakes — a Review of Current Knowledge

Abstract We review existing information on lake trout spawning habitat, which might indicate whether habitat is now a limiting factor in lake trout reproductive success. Lake trout spawning habitat quality is defined by the presence or absence of olfactory cues for homing, reef location with respect to the shoreline, water depth, proximity to nursery areas, reef size, contour, substrate size and shape, depth of interstitial spaces, water temperature at spawning time, water quality in interstitial spaces, and the presence of egg and fry predators. Data on factors which attracted native spawners to spawning reefs are lacking, due to the absence of historic data on egg deposition. No direct evidence of egg deposition has been collected from sites deeper than 18 m. Interstitial space and, therefore, substrate size and shape, appear to be critical for both site selection by adults and protection of eggs and fry. Water quality is clearly important for egg incubation, but the critical parameters which define water quality have not yet been well determined in the field. Exposure to wave energy, dictated in part by reef location, may maintain high water quality but may also damage or dislodge eggs. The importance of olfactory cues, water temperature, and proximity to nursery habitat to spawning trout is unclear. Limited data suggest that egg and fry predators, particularly exotic species, may critically affect fry production and survival. Although availability of physical spawning habitat is probably not limiting lake trout reproduction, changes in water quality and species composition may negatively affect early life stages. This review of habitat factors that affect early life stages of lake trout suggests several priorities for research and management.

Changes in Lake Trout Growth and Abundance after Introduction of Cisco into Lake Opeongo, Ontario

Abstract We examined changes in annual age-specific growth rates of 0–8-year-old lake trout Salvelinus namaycush in Lake Opeongo, Ontario, after the introduction of cisco Coregonus artedii into the lake in 1948. Growth rates of piscivorous lake trout (ages 3–8) initially increased as the occurrence of ciscoes increased, and then decreased as the abundance of piscivorous lake trout increased and the size of ciscoes eaten decreased. Growth of non-piscivorous 1- and 2-year-old lake trout decreased as the occurrence of insects decreased and the abundance of 1- and 2-yearold fake trout increased. Prey abundance, prey size, and intraspecific competition appeared to be major factors influencing growth rates. As ciscoes came to dominate the diet of adult lake trout, cannibalism by adults on younger lake trout decreased, as did the mortality suffered by young lake trout. The cisco introduction improved the existing sport fishery for lake trout by raising annual maximum sustainable yield from about 0.18 kg/hectare ...

Survival and Growth of Stocked Lake Trout in Relation to Body Size, Stocking Season, Lake Acidity, and Biomass of Competitors

Abstract Juvenile, hatchery-reared lake trout Salvelinus namaycush, 25–36 months old, were stocked (about 24 fish/hectare) in six small oligotrophic lakes to test the effects of fish size, stocking season, and lake water acidity on survival and growth of introduced fish. The test lakes had few, if any, native lake trout. Little or no survival of stocked lake trout occurred in lakes with pH 5.0 or less. High survival and growth occurred in intermediately acidic (pH 5.6–6.1) and circumneutral (pH 6.9–7.3) lakes. Survival of stocked lake trout increased with size at the time of stocking. Size differences of the three size-classes introduced in each lake were maintained throughout the 2-year study. Competition with other resident fish species appeared to influence stocking success strongly. There was an inverse relationship between the biomass of stocked lake trout subsequently recaptured and biomass of all hypolimnefic species present in the lake. Intraspecific competition with previously stocked lake trout ...

Survival and Development of Lake Trout Eggs and Fry in Eastern Lake Ontario — in situ Incubation, Yorkshire Bar, 1989–1993

Restricted production of lake trout fry in eastern Lake Ontario limits recruitment and the establishment of a self-sustaining population. To examine the survival and development of eggs and fry, incubation studies were conducted from 1989 to 1993 in situ on Yorkshire Bar and in the laboratory with untreated surface water from Lake on the Mountain. Eggs were collected at spawning time (16 October–9 November, median 24 October) from Lakes Ontario and Manitou, fertilized, and held individually for an average of 162 days in 290 50-cell Plexiglas incubation chambers. On Yorkshire Bar, significantly more eggs died (P < 0.001, 1.65× mean absolute difference (Δx¯) = 14%), and regardless of egg source, there were fewer hatched fry than in the laboratory (P < 0.001, 0.63×, Δx¯ = 29%); 75% of the fry that hatched died early in the incubation period, and 42% of these completely decomposed and disappeared by the end of the incubation period, leaving empty incubation cells. Significantly fewer live fry were produced on Yorkshire Bar than in the laboratory (11.2% versus 69.2%, Δx¯ = 58%). Abundance of live fry was inversely related to cumulative thermal units (CTU). Increased exposure on the bar from 370 to 690 CTU decreased survival from 25% to 0. In eastern Lake Ontario, spawning has been observed at a mean water temperature of 11.5°C (29 October) but ranged between 12.7°C (19 October) and 8.8°C (14 November); fry survival on 1 May from these dates and temperatures would be 10%, 0%, and 21%, respectively. If the mean temperature at spawning were 2°C lower (9.5°C, 9 days later), production of fry on 1 May would be almost double (19% vs.10%). Spawning at lower temperatures would increase fry production on shoals like Yorkshire Bar. Temperature inversely affects fry survival, especially if the spawning substrate is degraded by organic sedimentation, which causes increased biological oxygen demand and reduces oxygen concentrations.

Otolith age determination for adult tilapia, Oreochromis niloticus L. from Lake Awassa (Ethiopian Rift Valley) by interpreting biannuli and differentiating biannual recruitment

Age of mature Oreochromis niloticus in Lake Awassa, Ethiopia, was estimated by analysing optical macrozones (translucent and opaque) in sagittal otoliths from fish sampled over a 12-month period. Seasonal record on the type of macrozone at the edge of otoliths suggested that two translucent macrozones associated with biannuli were formed each year; one during January and February and another during June and July. Formation of translucent macrozones coincided with minimum water temperature, spawning associated loss in condition and presumably with reduction in the quantity and quality of the food consumed by the fish. Relative marginal increment analysis showed that biannulus formation may be completed in March and in August each year. A concurrent study has confirmed a biannual recruitment in O. niloticus in Lake Awassa, from which mid-February and mid-August were taken as median hatch-dates. A procedure to assign otolith age is described which considers median hatch-dates and uses the number of biannuli in otoliths without discriminating between fish from the two recruitment cohorts. We also show a procedure to discriminate between the two cohorts by using the number of biannuli, conditions on the edge of the otolith and time of capture to assign age for the two recruitment cohorts separately.

Growth and Ultimate Length of Muskellunge from Ontario Water Bodies

Abstract Growth of muskellunge Esox masquinongy from 12 Ontario sources was investigated by examining 582 samples from the Cleithrum Project archive and other specific studies; 88% of the samples were from angler-caught “trophy” fish. We detail sampling problems and develop methods for resolving them. Muskellunge from some sources were unsexed; sex was discriminated (probability of correct classification, 98.3%) from the von Bertalanffy growth parameters ultimate length (L∞) and growth coefficient, K. When one sex was inadequately sampled, the von Bertalanffy growth parameters of one sex were used to estimate those of the other. When samples were small and inadequate (<11), we used concordance sum of squares to match growth and give an interim estimate from the adequately sampled source with the best growth match. In Ontario populations, mean ultimate total lengths range widely: from 81.4 to 140.0 cm for females and from 70.7 to 115.9 cm for males. Females can be grouped into three types of growth, produc...

Use of Egg Traps to Investigate Lake Trout Spawning in the Great Lakes

Disk-shaped traps were used to examine egg deposition by lake trout (Salvelinus namaycush) at 29 sites in the Great Lakes. The main objectives were to; first, evaluate the disk trap as a device for sampling lake trout eggs in the Great Lakes, and second, summarize what has been learned about lake trout spawning through the use of disk traps. Of the 5,085 traps set, 60% were classified as functional when retrieved. Evidence of lake trout egg deposition was documented in each of the lakes studied at 14 of 29 sites. A total of 1,147 eggs were trapped. The percentage of traps functioning and catch per effort were compared among sites based on depth, timing of egg deposition, distance from shore, size of reef, and type of reef (artificial or natural). Most eggs were caught on small, shallow, protected reefs that were close to shore. Use of disk traps on large, shallow, unprotected offshore reefs or along unprotected shorelines was generally unsuccessful due to the effects of heavy wind and wave action. Making multiple lifts at short intervals, and retrieval before and re-deployment after storms are recommended for use in exposed areas. On large reefs, preliminary surveys to identify preferred lake trout spawning habitat may be required to deploy disk traps most effectively. Egg deposition by hatchery-reared fish was widespread throughout the Great Lakes, and the use of artificial structures by these fish was extensive.

Reappearance of Deepwater Sculpin in Lake Ontario: Resurgence or Last Gasp of a Doomed Population?

ABSTRACT Deepwater sculpin (Myoxocephalus thompsonii) were abundant in Lake Ontario in the 1920s and at least common into the 1940s. By the 1960s they were rare and, thereafter, some considered the population extirpated even though a synoptic survey of the lake in 1972 produced three, relatively large (148–165 mm total length, TL), and presumably old, specimens from the northern half of the lake. Deepwater sculpin were absent from annual survey catches in the 1980s and did not reappear until 1996, when three were caught in northern Lake Ontario. Isolated collections of deepwater sculpin continued during 1998–2004. Catches during 1996–2004 included five smaller individuals, 89–118 mm TL. In 2005, catches increased sharply, with 18 deepwater sculpin collected from southern waters and one from northern waters. Moreover, young, small sculpin were dominant in 2005—16 of the 19 sculpins averaged 68 ± 12 mm total length (± 1 s.d.). The young fish observed since 1996 could have originated from reproduction by the small in-lake population, from downstream drift of planktonic larvae from Lake Huron, or both. The presence of juveniles is a clear sign that conditions for survival of young deepwater sculpin are becoming more favorable, perhaps because of reduced abundance of alewife (Alosa pseudoharengus), a pelagic planktivore linked to depression of deepwater sculpin in Lake Michigan, and also low abundances of burbot (Lota lota) and lake trout (Salvelinus namaycush), benthic piscivores.