Diadromous Fish Species Research Articles

Effect of fall height and notch shape on the passage of inanga (Galaxias maculatus) and common bullies (Gobiomorphus cotidianus) over an experimental weir

The effect of fall height and notch shape on fish passage over an experimental weir was evaluated for two native diadromous fish species, the common bully (Gobiomorphus cotidianus) and adult and juvenile inanga (Galaxias maculatus). Juvenile inanga and common bullies were restricted by falls of 10 cm or higher whereas adult inanga were not restricted until a fall height of 20 cm was reached. Notch shape had a significant effect on common bully passage, with fish negotiating the v‐notch weir more easily than the rectangular or circular weirs. There was no real effect of notch shape on adult inanga passage, although juvenile inanga were restricted by a wide rectangular weir. The size of common bullies and adult inanga affected their passage, with larger fish surpassing the weirs with greater ease than smaller fish. The length of juvenile inanga did not influence their ability to pass the weirs. Fall height, rather than notch shape was the greatest factor restricting passage of both species, although the amount of turbulence below the weir may be a factor influencing the ability of fish to negotiate weirs.

11-Oxygenated androgens in female teleosts: prevalence, abundance, and life history implications

Although 11-ketotestosterone (11-KT) has been found in blood of females of several diadromous fish species, the importance, abundance, and prevalence of this and related 11-oxygenated androgens in females have not been investigated. To address this issue and to determine whether the differences among androgen profiles relate to specific life history strategies, particularly diadromous migrations, fish (males and females) of around 30 species were sampled and 5 androgens were measured by radioimmunoassay. Levels of 17β-estradiol and cortisol were also determined to evaluate ovarian and interrenal activity at the time of sampling. Testosterone (T) was the predominant androgen in most sexually recrudescent females. Only in female eel and sturgeon were 11-oxygenated androgens present in levels as high as, or higher than, those of T, although substantial amounts were also found in blood of mullet and salmonids. 11-KT was generally the most abundant 11-oxyandrogen, levels being higher than those of 11β-hydroxytestosterone or 11β-hydroxyandrostenedione. It is concluded that 11-oxygenated androgens are quantitatively minor steroids in most female fish. There was no convincing evidence to support the notion that the presence of 11-oxygenated androgens in blood is an adaptation specific to migratory fishes.

Downstream Migration of Juvenile European Sturgeon Acipenser sturio L. in the Gironde Estuary

The European sturgeon (Acipenser sturio) is an endangered diadromous fish species that spawns in the rivers in late spring and early summer. The juveniles spend their first years in the brackish waters (5‰ to 25‰) of the estuary zone before moving out to sea. This study describes the downstream migration pattern of juvenile sturgeon, belonging to the 1994 cohort, the only one born naturally in the Gironde basin, France since the end of the 1980s. During October 1994 to December 1996 the inland section of the Gironde estuary was sampled monthly by trawl (n=818 tows) and all European sturgeon caught (n=381) were marked and released. The first sturgeon of the 1994 cohort (TL=27 cm) were caught in early March 1995 in the zones furthest upstream. During their second fall of life, juveniles gradually acclimatized, and spread over a wide range of salinity conditions. A first incursion into marine water was also observed (at least for a few fish) by the end of the second winter. During this second period, sturgeon showed preference for two particular zones situated at 18 and 38 km, respectively, from the mouth of the estuary. These zones, belonging to two different salinity sectors of the estuary, did not appear to be any different to their neighbors with regards to depth and type of substrate. There were no significant size differences among estuarine zones. Seasonal movements of sturgeon seem to be motivated by a search for warmer temperatures. After a period of early acclimatization of 15 months, juvenile European sturgeon appear to be highly tolerant of salinity variations.

Reduced abundance of banded kokopu (Galaxias fasciatus) and other native fish in turbid rivers of the North Island of New Zealand

Laboratory experiments demonstrated that migrant juvenile banded kokopu (Galaxias fasciatus Gray) were more sensitive to suspended sediment (SS) than other native fish species. If juvenile migrants avoid waters made turbid by SS and their recruitment to adult habitats up stream is reduced, then adult abundance may decline in turbid rivers. To test this, we compared the abundance of diadromous native fish between turbid and clear rivers. The duration (% time) for which SS concentrations exceeded 120 mg litre‐1 (a critical level from laboratory experiments) during the migration season (August‐December) was estimated for over 150 New Zealand river sites. Turbid rivers were defined as those where SS concentrations exceeded 120 mg litre‐1 for over 20% of the time and clear rivers as those where SS concentrations exceeded 120 mg litre‐1 for less than 10% of the time. Eight turbid rivers and seven clear ones were identified where sufficient data on SS and native fish populations existed to permit a comparison. The mean occurrence of banded kokopu was reduced by 89.5% in turbid rivers and, although other diadromous fish species were also less common, banded kokopu was most affected. Densities of adult banded kokopu were also significantly lower in optimal stream habitats in three turbid compared with three matched clear rivers. We therefore concluded that the abundance of adult banded kokopu was reduced in turbid rivers and propose that this is because of reduced recruitment of juveniles in turbid rivers.

Diadromy and longitudinal patterns of upstream penetration of freshwater fish in Taranaki, New Zealand

Diadromous fish species dominate the New Zealand freshwater fish fauna and make up 15 of the 17 native fish species found on the Taranaki Ring Plain. Trajectories of occurrence in relation to elevation and distance from the sea are described for 11 diadromous and 2 non‐diadromous species using data from the New Zealand Freshwater Fish Database and data collected over the summer of 1997/ 98. Distinctive distributions were found for most of the species related to their differing migratory strategies and abilities. The species were ranked based on components of these trajectories to compare their penetrative ability. Comparison of the ranking methods used revealed they produced similar results. The ranking of the 11 diadromous species in Taranaki relative to each other revealed similar rankings to those for the same species from the West Coast of the South Island. The non‐migratory native fish, Cran's bully (Gobiomorphus basalis), was not found on the western side of the mountain. This distribution is thought to be the result of the local extinction of non‐migratory species in high gradient or unstable streams.

The evolution of diadromy in fishes (revisited) and its place in phylogenetic analysis

Diadromy is a term used to describe migrations of fishes between fresh waters and the sea; these migrations are regular, physiologically mediated movements which occur at predictable life history phases in each diadromous species, they involve most members of a species' populations, and they are usually obligatory. Around 250 fish species are regarded as diadromous. A review of the life history strategies amongst families of fishes that include diadromous species provides little support for a suggested scenario for their evolution that involves: (1) evolution of anadromy via amphidromy from fishes of marine origins, and (2) evolution of catadromy through amphidromy from fishes of freshwater origins, even though these scenarios seem intuitively reasonable. The various forms of diadromy appear to have had multiple independent origins amongst diverse fish groups. There is increasing confidence that behavioural characteristics of animals are heuristic in gener ating and interpreting phylogenies. However, examination of fishes shows wide variability of diadromous life histories within closely related families and genera, within species, and there is even ontogenetic variation in patterns of behaviour by individual fish. In addition, there is multiple loss of diadromy in many diadromous fish species in which the life history becomes restricted to fresh waters. This variation suggests that diadromy is a behavioural character of dubious worth in determining phylogenetic relationships. Moreover, it appears to have been an ancestral condition in some fish families, such as Anguillidae, Salmonidae, Galaxiidae, Osmeridae, and others, and perhaps in the whole salmonoid/osmeroid/galaxioid complex of families. This, too, makes diadromy of dubious worth in phylogenetic analysis

Habitat Models for Nesting Bald Eagles in Maine

We derived habitat models for nesting bald eagles (Haliaeetus leucocephalus) in river, lake, marine mainland, and marine island habitats. We measured 39 variables and used discriminant analysis to contrast 82 occupied nest sites and 88 random sites in Maine. Compared to random sites, bald eagle nests were located on river stretches with a larger basin area, less forest edge, and closer to the shore. The lake model indicated that bald eagle nests were positively associated with the number of superdominant trees and negatively associated with distance to water, area of land disturbed by humans, and area of land harvested for timber. The number of diadromous fish species and area of water <1.8 m deep at low tide were positively associated with bald eagle nests in marine mainland habitats; length of roads near nests was a negative variable. Nests were located on smaller marine islands than were random points (P < 0.005), resulting in nesting islands characterized by larger terrestrial and aquatic openings in the forest canopy, less forest edge, and a smaller area of combined shallow water and intertidal area. Correct classification rates for models varied from 75% for the marine island model to 100% for the river model. Similar classification rates, which never differed by more than 8%, occurred during cross validation. Validity of marine models was further suggested by the establishment of 4 bald eagle nests 51.9 km from random sites classified as nest sites; no nests have been established ?1.9 km from random sites classified as unused.