Jonathan Heifetz

Effects of Logging on Winter Habitat of Juvenile Salmonids in Alaskan Streams

Abstract Effects of logging on preferred winter habitats of juvenile salmonids in southeastern Alaskan streams were assessed by comparing the area of preferred winter habitat in 54 reaches of 18 streams. Three types of streams were sampled at each of six locations: a stream in a mature, undisturbed forest; a stream in a clear-cut area but logged on at least one bank; and a stream in a clear-cut area with strips of forest (buffer strips) along the stream bank. To identify preferred winter habitats, we classified stream areas in 12 of 18 streams into discrete habitat types and compared the density of salmonids within these habitat types with average density of the entire reach. Most wintering coho salmon (Oncorhynchus kisutch), Dolly Varden (Salvelinus malma), and steelhead (Salmo gairdneri) occupied deep pools with cover (i.e., upturned tree roots, accumulations of logs, and cobble substrate). Riffles, glides, and pools without cover were not used. Seventy-three percent of all pools were formed by large or...

Effects of Logging on the Abundance and Seasonal Distribution of Juvenile Steelhead in Some Southeastern Alaska Streams

Abstract Eighteen streams in six locations in southeastern Alaska were examined for the effects of logging on juvenile steelhead (Salmo gairdneri) populations. Three types of streams were examined at each location: a stream in undisturbed old-growth forest; a stream in a clear-cut area with strips of forest (buffer strips) along the stream bank; and a stream in a clear-cut area logged on at least one bank. Within each stream type, three reaches were sampled. Few juvenile steelhead were found in reaches where juvenile cutthroat trout (Salmo clarki) were present, and no juvenile steelhead were found in streams with a low-flow discharge (<0.06 m 3/s). Only two study sites, Prince of Wales Island and Mitkof Island, had juvenile steelhead in all three stream types. Fry (age 0) and parr (age I and older) were sampled in summer and winter at the Prince of Wales Island site; parr were sampled in summer at the Mitkof Island site. Logging appeared to affect the growth of steelhead fry and the abundance and distribu...

Two Genetically Distinct Forms of Rougheye Rockfish Are Different Species

Abstract The variation in mitochondrial DNA (mtDNA) and at eight microsatellite loci was analyzed in 700 rougheye rockfish Sebastes aleutianus sampled along the Pacific Rim from the Oregon coast to the western Aleutian Islands and Bering Sea. The program STRUCTURE was used to analyze the microsatellite genotypes and determine that the samples probably came from two genetically distinct sources (type I and type II) by minimizing the strong Hardy−Weinberg and gametic disequilibria observed in the total sample. The two types had nearly fixed differences at one microsatellite locus (μSma 6), which corresponded to divergent mtDNA haplotype clusters. We conclude that these two types are distinct species. The ranges of the two types overlapped but were not coincident; in some areas, one or the other predominated. For example, most of the Aleutian Island samples were type I fish. Although both types were caught in the same hauls in some regions, often one or the other species was predominant in a haul. The differ...

Decision analysis of alternative harvest policies for the Gulf of Alaska Pacific Ocean Perch Fishery

By the mid-1970s the estimated biomass of Pacific ocean perch (POP), Sebastes alutus, in the Gulf of Alaska (GOA) had been reduced to about 10% of the estimated level present during the early 1960s. Although fishing mortality was greatly reduced, the stock has shown only modest increases in biomass; the current estimate of spawner biomass is between 15% and 20% of the estimated peak levels. This decline has raised concern that past management measures may have been inadequate to allow growth of the POP stock in the GOA. Consequently, we performed an analysis to: (a) identify optimal fishing rates for rockfish species such as Pacific ocean perch, (b) identify the biomass level that would produce an optimum yield, and (c) evaluate alternative fishing policies designed to improve the condition of the POP resource. The selection of an optimal fishing rate for POP in the GOA was based on a maximin criterion. Recruitment variability was shown to play an important role in determining the effects of different harvest policies. Based on estimates of optimal biomass and fishing mortality rates, four alternative harvest policies were developed and evaluated using a stochastic simulation model. These policies ranged from harvests based on rates under the status quo policy to increasingly restrictive measures. Policy outcomes were measured in terms of yield in weight and dollar-value, female spawner biomass, and risks. We presented the results in the form of Bayesian decision tables. The ability to predict future stock levels with a high degree of certainty is poor. In no case is there a guarantee that rebuilding will occur.

Population structure of Alaskan shortraker rockfish, Sebastes borealis, inferred from microsatellite variation

Alaskan shortraker rockfish population structure was analyzed by examining allelic variation at eight microsatellite loci. Samples were collected along the continental shelf and upper slope from the south end of Baranof Island to the western Aleutian Islands, and collections were pooled into eight geographically distinct groups. An exact test of homogeneity indicated population structure (p < 0.0006) among groups. The proportion of the total variation that was attributable to divergence among populations (θ = 0.0014) was not statistically significant, and no evidence of a geographic cline of structure was detected. Finer scale analyses that compared adjacent collections indicated that the collection from the southern end of the range differed from all remaining collections at three loci. Structure related to geographic location was detected by partitioning the variation among populations. The size distributions of shortraker rockfish varied among collections from east to west. The size differences may reflect divergent oceanographic and biological factors acting on populations that have restricted migration and movement. Alternatively, if there is substantial movement accompanied by lengthy reverse migration to natal grounds, the size differences may be related to ages of cohorts that are differentially distributed along the Pacific Rim. Further biological information including size, age composition, and age of maturity data, as well as information on other life history characteristics will be required to explain shortraker rockfish population structure.

Identification and First Documentation of Larval Rockfishes in Southeast Alaskan Waters Was Possible Using Mitochondrial Markers but Not Pigmentation Patterns

Abstract More than 30 species of rockfish (genus Sebastes) occur in Alaskan waters, but their larvae generally cannot be identified by morphology. Consequently, knowledge of life histories is incomplete for this commercially and ecologically valuable taxon, and the locations and habitats of the larvae of specific species have not been determined. We used mitochondrial DNA markers, which now can delineate most Alaskan rockfishes, to identify larvae collected in ichthyoplankton surveys conducted in Southeast Alaskan waters. We report the occurrence of 15 species or species groups. Sebastes zacentrus (sharpchin rockfish), S. proriger (redstripe rockfish), and members of the indistinguishable group S. variegatus (harlequin rockfish)−S. wilsoni (pygmy rockfish)−S. emphaeus (Puget Sound rockfish) were observed every year and in most collections in Chatham Strait and along western Prince of Wales Island. Sebastes zacentrus was abundant only in Chatham Strait; S. auriculatus (brown rockfish) and S. elongatus (gre...

Do Genetically Distinct Rougheye Rockfish Sibling Species Differ Phenotypically

Abstract Two cryptic species of rougheye rockfish Sebastes aleutianus, which we refer to as types I and II, have been identified independently from DNA (microsatellite and mitochondrial DNA [mtDNA]) markers and from distributions of allozyme allele frequencies. Visual differences that discriminate between these species in the field would improve their conservation and management. To delineate species, we used two microsatellite loci, μSma6 and μSma7, in conjunction with mtDNA site differences for the restriction enzymes Cfo I in the region of NADH dehydrogenase (ND) subunits 3 and 4 and Mbo I in the region of ND subunits 5 and 6. We compared meristic characters and morphological dimensions of the genetically determined species and observed that although all parameters had overlapping distributions, type II rougheye rockfish have slightly fewer and shorter gill rakers and deeper bodies. Discriminant analysis of morphological characteristics accurately delineated the species (>94%). Rougheye rockfish have t...