Hybridization between distinct populations of salmon can cause fitness loss (outbreeding depression), and may result in reduced survival. The erosion of fitness-related traits such as homing ability and change in family size distribution may underlie reduced survival. Outbreeding depression was investigated in two independent experiments that made hybrids between geographically separated and genetically divergent pink salmon populations. Control crosses were made from male and female Auke Creek (Southeast Alaska) pink salmon and hybrid crosses were between Auke Creek females and Pillar Creek (Kodiak Island, about 1000km away) males. Parentage assignment from microsatellite analysis improved estimates of survival and straying, and was used to examine variation in family size. The return rates of even-broodyear Fi control and hybrid fish were similar, but the odd-broodyear Fj control returns exceeded hybrid returns. The F2 control returns exceeded hybrid returns in both the even-and oddbroodyears. Hybridization did not impair homing ability; weekly surveys in nearby (~ 1km) Waydelich Creek revealed similar straying rates from Auke Creek by both hybrid and control fish in all years. Family data were available only for even-broodyear returns; hybridization did not increase the index of variability (ratio of variance to mean) in family size in these years. Outbreeding depression in hybrids of geographically separated populations demonstrates the potential for introgression of normative fish to erode natural production.

Hybridization between distinct populations of salmon can cause fitness loss (outbreeding depression), and may result in reduced survival. The erosion of fitness-related traits such as homing ability and change in family size distribution may underlie reduced survival. Outbreeding depression was investigated in two independent experiments that made hybrids between geographically separated and genetically divergent pink salmon populations. Control crosses were made from male and female Auke Creek (Southeast Alaska) pink salmon and hybrid crosses were between Auke Creek females and Pillar Creek (Kodiak Island, about 1000km away) males. Parentage assignment from microsatellite analysis improved estimates of survival and straying, and was used to examine variation in family size. The return rates of even-broodyear Fi control and hybrid fish were similar, but the odd-broodyear Fj control returns exceeded hybrid returns. The F2 control returns exceeded hybrid returns in both the even-and oddbroodyears. Hybridization did not impair homing ability; weekly surveys in nearby (~ 1km) Waydelich Creek revealed similar straying rates from Auke Creek by both hybrid and control fish in all years. Family data were available only for even-broodyear returns; hybridization did not increase the index of variability (ratio of variance to mean) in family size in these years. Outbreeding depression in hybrids of geographically separated populations demonstrates the potential for introgression of normative fish to erode natural production.

No abstract

Seven segments of mitochondrial DNA (mtDNA), comprising 97% of the mitochondrial genome, were amplified by polymerase chain reaction (PCR) and examined for restriction site variation using 13 restriction endonucleases in three species of Pacific salmon: pink (Oncorhynchus gorbuscha), chum (O. keta) and sockeye (O. nerka) salmon. The distribution of variability across the seven mtDNA segments differed substantially among species. Little similarity in the distribution of variable restriction sites was found even between the mitochondrial genomes of the even- and odd-year broodlines of pink salmon. Significantly different levels of nucleotide diversity were detected among three groups of genes: six NADH-dehydrogenase genes had the highest; two rRNA genes had the lowest; and a group that included genes for ATPase and cytochrome oxidase subunits, the cytochrome b gene, and the control region had intermediate levels of nucleotide diversity. Genealogies of mtDNA haplotypes were reconstructed for each species, based on the variation in all mtDNA segments. The contributions of variation within different segments to resolution of the genealogical trees were compared within each species. With the exception of sockeye salmon, restriction site data from different genome segments tended to produce rather different trees (and hence rather different genealogies). In the majority of cases, genealogical information in different segments of mitochondrial genome was additive rather than congruent. This finding has a relevance to phylogeographic studies of other organisms and emphasizes the importance of not relying on a limited segment of the mtDNA genome to derive a phylogeographic structure.

Visual survey by divers using open-circuit (OC) SCUBA is the most widely used approach to survey coral reef fishes. Therefore, it is important to quantify sources of bias in OC surveys, such as the possibility that avoidance of OC divers by fishes can lead to undercounting in areas where targeted species have come to associate divers with a risk of being speared. One potential way to reduce diver avoidance is to utilize closed circuit rebreathers (CCRs), which do not produce the noise and bubbles that are a major source of disturbance associated with OC diving. For this study, we conducted 66 paired OC and CCR fish surveys in the Main Hawaiian Islands at locations with relatively high, moderate, and light fishing pressure. We found no significant differences in biomass estimates between OC and CCR surveys when data were pooled across all sites, however there were differences at the most heavily fished location, Oahu. There, biomass estimates from OC divers were significantly lower for several targeted fish groups, including surgeonfishes, targeted wrasses, and snappers, as well as for all targeted fishes combined, with mean OC biomass between 32 and 68% of mean CCR biomass. There were no clear differences between OC and CCR biomass estimates for these groups at sites with moderate or low fishing pressure, or at any location for other targeted fish groups, including groupers, parrotfishes, and goatfishes. Bias associated with avoidance of OC divers at heavily fished locations could be substantially reduced, or at least calibrated for, by utilization of CCR. In addition to being affected by fishing pressure, the extent to which avoidance of OC divers is problematic for visual surveys varies greatly among taxa, and is likely to be highly influenced by the survey methodology and dimensions used.

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 HardyϪWeinberg and gametic disequilibria observed in the total sample. The two types had nearly fixed differences at one microsatellite locus (Sma 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 differences in distributions suggest a historic vicariant or ecological basis for their divergence. No phenotypic characteristics have been confirmed that can be used to distinguish the two species visually. Rougheye rockfish have high commercial value and their incidental catch has the potential to greatly affect larger fisheries. The discovery of cryptic speciation in a commercially important species underscores our need to learn more about the distribution and biology of these and other groundfish species.

Extinction risk is closely tied to body size, home range, and species distribution. Quantifying home range is critical for conservation, and can enable the use of concepts such as 'umbrella species', whose conservation protects other species due to shared habitat. To determine the value of the humphead wrasse as an umbrella species for coral reef conservation, we conducted a multi-year study of humphead wrasse home range at Palmyra Atoll, Central Tropical Pacific, tagging juvenile, female, and male individuals with acoustic transmitters. We quantified home range using 2 metrics, length and area, and determined if these metrics were related to the sex and maturity status of the individual. We recorded individual movements during 5030 fishdays, yielding detailed records for 14 individuals comprising 3 juveniles, 5 females, and 6 males. The home range of humphead wrasse measured over a 2 yr study was 0.4 to 14 km and changed with ontogeny. Females had larger home ranges than other reef fishes studied to date (n = 68), indicating value as an umbrella species for coral reefs. We compared the home range of the species to the size distribution of tropical marine protected areas (MPAs), and used a model to estimate the MPA length necessary to retain humphead wrasse. Most MPAs are too small to effectively protect the humphead wrasse.

As the threats to coral reefs mount, scientists and managers are looking for innovative ways to increase the scope, scale, and efficiency of coral reef monitoring. Monitoring changes in coral communities and demographic features provides key information about ecosystem function and resilience of reefs. While most monitoring programs continue to rely on in-water visual survey methods, scientists are exploring 3D imaging technologies such as photogrammetry, also known as Structure-from-Motion (SfM), to enhance precision of monitoring, increase logistical efficiency in the field, and generate a permanent record of the reef. Here, we quantitatively compare data generated from in-water surveys to SfM-derived metrics for assessing coral demography, bleaching, and diversity in the main Hawaiian Islands as part of NOAA’s National Coral Reef Monitoring Program. Our objectives were to compare between-method error to within-method error, test for bias between methods, and identify strengths and weaknesses of both methods. Colony density, average colony diameter, average partial mortality, prevalence of bleaching, species richness, and species diversity were recorded using both methods within the same survey areas. For all metrics, the magnitude of between-method error was comparable to the within-method error for the in-water method and between method error was significantly higher than within-method error for SfM for one of the seven metrics. Our results also reveal that a majority of the metrics do not vary significantly between methods, nor did we observe a significant interaction between method and habitat type or method and depth. Exceptions include estimates of partial mortality, bleaching prevalence, and Porites juvenile density–though differences between methods are generally small. Our study also highlights that SfM offers a unique opportunity to more rigorously quantify and mitigate inter-observer error by providing observers unlimited “bottom time” and the opportunity to work together to resolve difficult annotations. However, the necessary investment in equipment and expertise does present substantial up-front costs, and the time associated with curating imagery, photogrammetric modeling, and manual image annotation can reduce the timeliness of data reporting. SfM provides a powerful tool to reimagine how we study and manage coral reefs, and this study provides the first quantified methodological comparison to validate the transition from standard in-water methods to SfM survey methods for estimates of coral colony-level surveys.