Variation in large-bodied fish-community structure and abundance in relation to water-management regime in a large regulated river

Variation in life-history traits (growth, condition, mortality and recruitment) and relative abundance of 11 large-bodied fish species was investigated among three water-management regimes (unimpounded, run-of-the-river and winter reservoirs) in the large regulated Ottawa River, Canada. If waterpower management had an effect on fishes, then (1) would be expected community structuring among water-management regimes and (2) species with similar life-history traits should be affected in a similar manner. Large-bodied fish communities were assessed using two different standard index-netting techniques, one using trap nets and the other gillnets. Community structure could be discriminated based on species caught in nets using holographic neural networks (78·8% correct overall classification rate using trap nets and 76·0% using gillnets); therefore, water-management regimes affected community structure in the Ottawa River. Littoral zone benthivores were significantly lower in abundance ( P < 0·001) or absent in winter reservoirs, whereas the abundance of planktivores or species that were planktivorous at young ages were significantly greater than in unimpounded river reaches. Growth, condition and mortality did not vary among reach types except smallmouth bass Micropterus dolomieu were in better condition in winter reservoirs than unimpounded reaches. Lake sturgeon Acipenser fulvescens recruitment was impaired in run-of-the-river reaches, whereas recruitment for other species that spawn in fast water was not affected.     

Habitat utilization of juvenile lake sturgeon, Acipenser fulvescens, in a large Canadian river

An increased understanding of the juvenile life history stage of the lake sturgeon, Acipenser fulvescens , has been recognized as a key requirement for improving conservation efforts for this once abundant species. The objectives of the current study were to develop an effective methodology for capturing juvenile lake sturgeon in a large riverine environment; to describe the physical habitat characteristics (depth, water velocity and substrate) associated with the areas where juvenile lake sturgeon were captured; and to determine basic population parameters (length, body mass and condition factor) for juvenile lake sturgeon captured in those areas. Gillnets (mesh sizes 25–108 mm) were used to sample the Winnipeg River, a large river in the northern extent of the species range, from 12 June to 6 November 2006. A total of 2154 juvenile (<530 mm FL) lake sturgeon were captured, which represented over 74% of the total fish catch. Moderate (51–108 mm) and small (25 mm) mesh gill nets were found to be efficient for sampling juvenile lake sturgeon, with the former capturing a wider range of sizes and the latter capturing fewer fish but resulting in decreased mortality. Juvenile lake sturgeon were captured at high densities in discrete areas characterized by water depths >13.7 m, detectable water velocities >0.20 m s⁻¹, and various substrate types.     

The effects of starvation on plasma free amino acid and glucose concentrations in lake sturgeon

The effect of starvation on the metabolism of the lake sturgeon Acipenser fulvescens was examined by measuring haematocrit, plasma glucose concentrations, and plasma free amino acids. Plasma was sampled on day 0, 10, 20, 45 and 60 of a 60-day starvation period. Haematocrit was observed to decrease with starvation indicating a decreased oxygen carrying capacity of the blood. Plasma glucose levels differed only at day 10, with a decrease in blood glucose level in the starved group. No differences were detected between groups for alanine, aspartate, and serine, while elevated levels were observed for glutamine throughout the experiment. An increase in arginine, tyrosine, valine, methionine, tryptophan, phenylalanine, glutamate, glycine, isoleucine, histidine and leucine, concentrations were observed after 45 days of starvation. The maintenance, or increased plasma levels, of glucogenic amino acids in combination with the maintenance of blood glucose concentrations indicates active gluconeogenic processes in the liver supported by muscle proteolysis.     

Comparison of methods to quantify metabolic rate and its relationship with activity in larval lake sturgeon Acipenser fulvescens

Until recently most studies have focussed on method development for metabolic rate assessment in adult and/or juvenile fish with less focus on measurement of oxygen consumption (ṀO₂) during early life history stages, including fast-growing larval fish and even less focus on nonteleostean species. In the present study we evaluated measurement techniques for standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope in an Acipenseriform, the lake sturgeon Acipenser fulvescens, throughout the first year of life. Standardized forced exercise protocols to assess MMR were conducted for 5 or 15 min before or after measurement of SMR. We used different levels of oxygen decline during the measurement period of MMR post forced exercise to understand the influence these may have on the calculation of MMR. Opercular rate and tail beat frequencies were recorded by video as measures of behaviours and compared to metabolic rate recorded over a 24 h period. Results indicate that calculated values for aerobic scope were lower in younger fish. Neither exercise sequence nor exercise duration influenced metabolic rate measurements in the younger fish, but exercise duration did affect measurement of MMR in older fish. Finally, there was no strong correlation between metabolic rate and the measured behaviours in the lake sturgeon at either age. Based on the results, we recommend that a minimum of 6 h of acclimation to the respirometry chamber should be given prior to measuring SMR, a chasing protocol to elicit MMR should ideally be performed at the end of experiment, a short chasing time should be avoided to minimize variation and assessment of MMR should balance measurement limitations of the probes along with when and for how long oxygen consumption is measured.     

水体中铜对中华鲟幼鱼血液生化指标的影响

通过检测中华鲟在不同铜离子浓度的水体中暴露60d后血液生化指标,研究Cu2+对幼鱼血浆生化成分和离子含量变化的影响及致毒效应.结果表明:中华鲟幼鱼血浆中血糖( Glu)、碱性磷酸酶(ALP)、尿素(Urea)、胆固醇(TC)、肌酐(CREA)含量随Cu2+浓度的增加而升高,低浓度组(0.40 μg· L-1)ALP含量与对照组有显著性差异(P＜0.05),Glu、Urea、TC、CREA含量无显著性差异;中浓度组(0.89 μg· L-1)和高浓度组(2.00 μg·L-1)含量与对照组均有显著性差异(P＜0.05).甘油三酯(TG)随着Cu2+浓度的增加而下降,低浓度组与对照组无显著性差异;中、高浓度组与对照组有显著差异(P＜0.05),总蛋白(TP)、谷草转氨酶(AST)、谷丙转氨酶(ALT)、乳酸脱氢酶(LDH-L)不受Cu2+的影响.Na+、Cl-、P含量和pH值随Cu2+浓度的增加而显著下降,Ca2+、Mg2+显著上升,其变化与Cu2+浓度存在相关性,K+含量不受Cu2+的影响.实验表明,Cu2+对中华鲟幼鱼血液生化指标的最低可观察效应浓度和最高无观察效应浓度分别为0.89和0.4 μg·L-1.血浆中ALP受Cu2+影响最明显,其含量除受Cu2+浓度影响外,随着时间的延长也显著升高,是Cu2+污染的敏感指标.     

Long-term phytoplankton changes in an artificially divided,top-down manipulated humic lake

Lake Große Fuchskuhle (Brandenburg, Germany) is a naturally acidic bog lake that was artificially divided into four basins by large plastic curtains for biomanipulation experiments in 1990. Different numbers of perch were added to each compartment beginning in the spring of 1993. The species composition and abundance of phytoplankton, pH, nutrient concentrations, dissolved organic carbon (DOC) and chlorophyll a content were analyzed at regular intervals during 1991 and 1998. The division of the lake resulted in divergent developments in the physical and chemical environment of the compartments. This study compared the phytoplankton assemblages of the Northeast- (NE) and Southwest- (SW) basins which differed strongly in chemistry during the investigation period. Divergent developments in phytoplankton species composition in both basins can be explained by changes in physical and chemical conditions (bottom-up effects). Increased pH values and DOC concentrations probably favoured mass developments of the dinoflagellate Gymnodinium uberrimum since 1993, while increased nutrients (dissolved inorganic carbon, total nitrogen and especially total phosphorus) as well as further changes in pH and DOC led to the dominance of the raphidophyte Gonyostomum semen in 1998. This bloom was characterized by extreme biomasses of up to 143 mg l^–1 wet weight, corresponding with high chlorophyll a concentrations of up to 413 g l^–1 at the same time. In contrast, no significant relationship between experimental manipulations by piscivorous fish stocking (top-down effects) and phytoplankton biomass were observed.     

Influence of prey condition and incubation method on mortality,growth and metabolic rate during early life history in lake sturgeon,Acipenser fulvescens

Environmental conditions during early life can have a profound impact on developmental trajectory and ultimately ecological fitness of individuals. Therefore, from a conservation perspective it is vital to understand the longer-term implications of early phenotypic development on survival. In this study, we examined the effects of temperature (maintained at 16°C or ambient river temperature), prey condition (live or dead Artemia) and incubation method (tumbling jar or natural hatching over substrate) on the routine or standard metabolic rate (RMR, SMR), maximum metabolic rate (MMR), factorial aerobic scope, energy density (ED), whole body triglyceride concentration (TG), growth and mortality rate of age-0 lake sturgeon. Our results demonstrated that fish fed live artemia had significantly lower ED, growth and high mortality rates than those fed dead artemia at 32 days post-fertilisation (dpf) (p < .001). However, at 133 dpf fish fed live artemia showed higher MMR and no difference in ED, TG and growth rate compared to those fed dead prey during early life history. The present study showed that inclusion of live prey at the onset of exogenous feeding may be considered to promote a more natural phenotypic development in larval lake sturgeon.     

Utilization of the exotic cladoceran Daphnia lumholtzi by juvenile fishes in an Illinois River floodplain lake

Daphnia lumholtzi comprises a substantial component of the zooplankton community during mid‐ to late‐summer in Lake Chautauqua, a floodplain lake along the Illinois River near Havana, Illinois. In order to quantify the utilization of D. lumholtzi by juvenile fishes, diet analyses were conducted for seven juvenile fish species collected from Lake Chautauqua during the 2001 annual drawdown period. Freshwater drum Aplodinotus grunniens and emerald shiner Notropis atherinoides demonstrated negative selectivity for D. lumholtzi relative to native zooplankton species whereas four species of fish (bluegill Lepomis macrochirus, white bass Morone chrysops, white crappie Pomoxis annularis and black crappie Pomoxis nigromaculatus) consumed substantial amounts of D. lumholtzi. Although selectivity values for D. lumholtzi varied among these fish species, positive selection for D. lumholtzi increased similarly among larger size classes of each fish species, and corresponded with ontogenetic shifts in diet. Mean body length of D. lumholtzi consumed by 20–69 mm L_T juvenile fishes ranged from 0·75 to 0·99 mm with a calculated total length range of 2·0–2·6 mm. Results from this study provide evidence that high abundances of D. lumholtzi in mid‐ to late‐summer provide an additional food source for several juvenile fish species during a time when abundances of large native cladoceran species (i.e. Daphnia) are low, and juvenile fishes are searching for larger prey associated with ontogenetic shifts from zooplankton to macroinvertebrates and fishes. Because zooplankton production is typically lower in rivers than in lakes, survivorship of juvenile fishes produced in floodplain lakes may be higher in riverine systems if they are not reliant on zooplankton as a primary food resource. Therefore, high abundances of D. lumholtzi may benefit juvenile fishes in managed floodplain lakes, such as Lake Chautauqua, by increasing growth and facilitating the transition from zooplanktivory to insectivory or piscivory.     

中国重要生态系统保护和修复工程区域植被覆盖时空变化研究

植被覆盖变化是气候变化和生态环境变化的双重指示器,如何量化全国尺度植被变化、评估生态修复成效,成为当前陆地表层生态系统研究领域共同的科学问题。利用2000—2020年的植被覆盖度(FVC)数据,采用增幅变化分析、Theil-Sen Median趋势分析、稳定性分析方法,对中国六大重要生态系统保护和修复工程区域的自然植被覆盖度本底和时空变化特征进行了研究,并对不同区域植被覆盖度变化与气温、降水的相关性进行了分析,以期掌握我国生态系统保护和修复“家底”。结果表明：(1)2020年,六大区域平均植被覆盖度为27.66%,2000—2020年,黄河重点生态区、北方防沙带和青藏高原生态屏障区增幅分别为54.4%、34.6%和21.8%,是全国范围平均植被覆盖度增幅的1.04—2.59倍;长江重点生态区、东北森林带和南方丘陵山地带增幅分别为18.0%、13.7%和12.9%,均低于全国增幅,我国西北方较南方改善更明显。(2)2000—2020年,六大区域植被覆盖度变化总体呈增加趋势。黄河重点生态区、东北森林带、南方丘陵山地带和长江重点生态区增加区域面积占比均超过60%,北方防沙带和青藏高原生态屏障...     

Identification of microsatellite loci in lake sturgeon,Acipenser fulvescens,and their variability in green sturgeon,A. medirostris

From (CATC)_n, (GATA)_n, (AAAC)_n, and (CA)_n–enriched libraries for the lake sturgeon Acipenser fulvescens, 254 primer pairs were developed. These primer pairs resulted in the identification of 128 microsatellite loci in either A. fulvescens or A. medirostris. Polymorphic loci were identified in both sturgeon species for 48 of the primer pairs and 14 of the primer pairs amplified polymorphic loci only in A. medirostris. Most of the identified loci appear to be tetrasomic (79.1% in A. fulvescens and 64.5% in A. medirostris). These results offer estimates of the degree of diploidization in each of these species.     

Interannual variation in effective number of breeders and estimation of effective population size in long‐lived iteroparous lake sturgeon (Acipenser fulvescens)

Quantifying interannual variation in effective adult breeding number (N_b) and relationships between N_b, effective population size (N_e), adult census size (N) and population demographic characteristics are important to predict genetic changes in populations of conservation concern. Such relationships are rarely available for long‐lived iteroparous species like lake sturgeon (Acipenser fulvescens). We estimated annual N_b and generational N_e using genotypes from 12 microsatellite loci for lake sturgeon adults (n = 796) captured during ten spawning seasons and offspring (n = 3925) collected during larval dispersal in a closed population over 8 years. Inbreeding and variance N_b estimated using mean and variance in individual reproductive success derived from genetically identified parentage and using linkage disequilibrium (LD) were similar within and among years (interannual range of N_b across estimators: 41–205). Variance in reproductive success and unequal sex ratios reduced N_b relative to N on average 36.8% and 16.3%, respectively. Interannual variation in N_b/N ratios (0.27–0.86) resulted from stable N and low standardized variance in reproductive success due to high proportions of adults breeding and the species' polygamous mating system, despite a 40‐fold difference in annual larval production across years (437–16 417). Results indicated environmental conditions and features of the species' reproductive ecology interact to affect demographic parameters and N_b/N. Estimates of N_e based on three single‐sample estimators, including LD, approximate Bayesian computation and sibship assignment, were similar to annual estimates of N_b. Findings have important implications concerning applications of genetic monitoring in conservation planning for lake sturgeon and other species with similar life histories and mating systems.     

Density, aggregation, and body size of northern pikeminnow preying on juvenile salmonids in a large river

Predation by northern pikeminnow Ptychocheilus oregonensis on juvenile salmonids Oncorhynchus spp. occurred probably during brief feeding bouts since diets were either dominated by salmonids (>80% by weight), or contained other prey types and few salmonids (<5%). In samples where salmonids had been consumed, large rather than small predators were more likely to have captured salmonids. Transects with higher catch-per-unit of effort of predators also had higher incidences of salmonids in predator guts. Predators in two of three reservoir areas were distributed more contagiously if they had preyed recently on salmonids. Spatial and temporal patchiness of salmonid prey may be generating differences in local density, aggregation, and body size of their predators in this large river.     

Repeat UCrit and endurance swimming in juvenile shortnose sturgeon (Acipenser brevirostrum)

Previous results show that juvenile shortnose sturgeon are steady swimmers and, compared with salmonids, generally have low critical swimming (UCrit) and endurance swimming capacities. Most studies on swimming capacities of sturgeon, and other fishes, include those where fish have only been swum once and the metrics of swimming performance are assessed (e.g., time swum, speed achieved). Under natural conditions, there are ample instances where fish undergo multiple swimming cycles when traversing fish ways, culverts and other sources of fast water flow. While some evidence exists for salmonids, the effects of repeat swimming are not well known for sturgeon. The current study consisted of two experiments. The first examined the UCrit of juvenile shortnose sturgeon following three consecutive swimming trials with a 30 min recovery period between subsequent tests. The second examined the endurance swimming capacities of juvenile shortnose sturgeon following three consecutive swimming trials with a 60 min recovery period between subsequent tests. Our findings indicate that (i) UCrit was consistent (~2 body lengths/s) among swimming trials; (ii) significant individual variation exists between individuals in the endurance swimming trials; and (iii) consistent results exist for individuals across swimming trials in both the UCrit and the endurance swimming tests. These results suggest that juvenile shortnose sturgeon have a high recovery capacity, and their behaviour and morphology likely reflect aspects of their swimming capacities.     

Annually laminated lake sediments and environmental changes in Bashang Plateau, North China

Angulinuo Lake is the biggest lake on the Bashang Plateau, North China, and is 47.6 km² in area and 2-6 m in depth. A core from the inner part of Angulinuo Lake was sliced and the sediment was observed by Scanning Electronic Microscope (SEM). Annual laminations characterized by variable color and grain size were found and interpreted as recording the cyclic deposition of lacustrine clay and aeolian dust. The results of chemical analysis of coarse grains conducted by SEM-EDAX, and grain size analysis of modern aeolian dust in the ice on Angulinuo Lake, support an aeolian origin for the light coarse layers. Image analysis technique was used to calculate the size and number of coarse grains in each layer. The coarse grains were fractionated into four classes: > 42 μm, 14-42 μm, 14-4.2 μm and 1.4-4.2 μm. In general, the abundance of the four classes shows similar temporal variation patterns. Around Angulinuo Lake, the winter monsoon is strong and transports aeolian dust into the lake. When the winter monsoon is strong, the size and amount of coarse grains are expected to increase. We infer that the winter monsoon was weaker during 8430-5440 year BP, and was unstable in the later part of this period. From 5440 year BP, the winter monsoon became stronger, and then weaker from 3250 to 2490 year BP. During 2490-1170 year BP, the winter monsoon was slightly stronger, but since 1170 year BP, it has become weaker again. The changes of the winter monsoon intensity recorded in the annual laminations in Angulinuo Lake sediments correspond well to environmental changes in North China and to changes in sea level during the same period. Periods of weaker winter monsoon correspond to times of higher sea levels while the periods of stronger winter monsoon correspond to the Neoglaciation stage in China and the periods of lower sea levels.     

Assessment of lake sturgeon (Acipenser fulvescens) recruitment in a regulated spawning tributary of Rainy Lake,Ontario

Continued study of the relationship between lake sturgeon (Acipenser fulvescens) recruitment and hydroelectric dams and operations, in a variety of river systems and habitat types is needed to improve the ability to predict and monitor impacts of the hydroelectric industry on this species. Herein, we present results of a juvenile lake sturgeon study aimed at addressing concerns over an inferred lack of recruitment resulting from spawning downstream of a hydroelectric generating station (HGS). Two years of sampling (2015 and 2016) were conducted in five sections of a 41 km long reach of the Seine River, Ontario, a lake sturgeon spawning tributary of Rainy Lake. Using an established gillnetting method, deepwater habitat was targeted to capture juvenile lake sturgeon to assess relative abundance, recruitment (cohort strength), and growth. Deepwater habitat, defined as water depths >6 m in this system, comprised only 2.1% of the wetted area in this study area. Within these habitats, a total of 331 lake sturgeon capture events were observed over the 2-years study period. The majority of the lake sturgeon catch (85%) was comprised of age-0 to age-5 individuals (both sampling years combined). Although inter-annual variation in cohort strength was apparent, each cohort between 2006 and 2016 was represented. The spatial distribution of cohorts varied among river reaches with younger individuals (age-0 and age-1) occupying reaches proximal to the Sturgeon Falls HGS, and larger, older individuals (age-2 to age-5) occupying reaches further downstream. The rarity of age-6+ individuals can likely be explained by ongoing downstream redistribution of juveniles over time, out of the Seine River and into Rainy Lake. Growth of juvenile lake sturgeon captured in the Seine River was above average relative to conspecifics from other rivers in the Hudson Bay drainage. Unfortunately, baseline data sets required to facilitate comparisons of contemporary (post-construction Sturgeon Falls HGS) versus historical (i.e. pre- Sturgeon Falls HGS) lake sturgeon recruitment, or to evaluate the influence of the Seine River Water Management Plan (2004) on lake sturgeon recruitment, are lacking. However, juvenile Lake Sturgeon are more abundant in this system than what had been surmised based on recent studies which implemented random sampling. Results indicate that juvenile lake sturgeon may reside in spawning tributaries for several years (age-0 to age-5) prior to seeking alternate habitats and highlights the value of targeted sampling (i.e. by depth) along the flow axis of rivers downstream of spawning areas when assessing lake sturgeon recruitment patterns.     

The effect of sub-lethal exposure to copper and the time course of recovery in clean water on biochemical changes in juvenile fish (Acipenser persicus)

This study reports the 96-h LC₅₀ value and tissue copper (Cu) levels and biochemical changes in juvenile fish (Acipenser persicus) exposed to 0.026?mg/l ambient Cu for 1, 7 and 14?days. It then examined the recovery of the same parameters after placing the juvenile fish in clean water for a further period of 28?days. The intestine, kidney and gill Cu levels, plasma glucose, total protein, triglyceride, cortisol, triiodothyronine and thyroxine concentrations, liver protein contents, liver catalase, superoxide dismutase (SOD) and glutathione S-transferase activities were studied. The 96-h LC₅₀ value of Cu was 0.502?mg/l for juvenile A. persicus. The results indicate that Cu exposure produced significant accumulations of Cu in gills and kidney over the treatment time. Sublethal dose of Cu resulted in a short-term increase in plasma glucose, total protein and cortisol levels that decreased with time. After the 28-day recovery phase, there were significant differences in kidney Cu levels and triglyceride concentrations as well as SOD activities between recovery fish treatments and their control groups on day 42. The 28-day recovery phase caused significant decreases in total protein levels and SOD activities of Cu-exposed fish on day 42 compared to day 14. The results suggest that 28?days are insufficient for complete recovery to Cu exposure by juveniles and a longer period would be required for full recovery. Moreover, the study showed that the recovery phase following Cu exposure could change biochemical parameters to levels that are not close to those seen during exposure or control levels.     

Distribution and seasonal abundance of benthic macroinvertebrates in a subtropical Florida lake

We studied the distribution and seasonal abundance of benthic macroinvertebrates from July 1975 through September 1976 in a hypereutrophic lake in subtropical Florida. The benthic community was comprised principally of oligochaetes (56.1%), chironomids (37.1%), and chaoborids (5.7%). Numbers of taxa and mean densities correlated negatively with depth and positively with mean grain size of the substratum and dissolved oxygen concentration at the mud-water interface. Seasonal abundances and life history information obtained for the predominant species of Chironomidae (Polypedilum halterale, Glyptotendipes paripes, Chironomus crassicaudatus, Cryptochironomus fulvus, C. blarina, Cladotanytarsus sp., Procladius culiciformis, and Coelotanypus concinnus) indicated that all of these species are multivoltine with rapid generation times. Larval lengths of life at summer temperatures, 27–31 °C, ranged from 14–22 days indicating that sampling in subtropical lakes should be at short intervals (approximately 3 days) if the life cycles, ecology, and function of the components of the benthic community is to be understood.     

浙江省环杭州湾产业带湿地时空动态

基于RS和GIS技术手段,采用土地利用动态变化的空间分析方法,对1990—2005年浙江省经济发展最活跃的环杭州湾产业带湿地的时空动态进行了研究.结果表明：研究期间,环杭州湾产业带内湿地与其他土地利用/覆被类型以及湿地内部地类之间的转化频繁,突出表现为湿地与农用地之间相互转化、建设用地占用湿地和杭州湾沿岸滩涂湿地转化为养殖水面;比较利益驱动和耕地占补平衡政策的双重影响,决定了环杭州湾产业带湿地时空动态的内在机制,即在水产养殖相对于传统农业的比较利益驱动下,大量内陆地区的农用地和杭州湾沿岸的滩涂湿地被开垦成养殖水面,而建设用地的迅速扩展、土地资源的紧张以及耕地占补平衡政策的实施导致湿地资源被侵占.     

Shifts in abundance and growth of slimy sculpin in response to changes in the predator population in an arctic Alaskan lake

Lake trout (Salvelinus namaycush) in Toolik Lake are tightly coupled to the benthos, since they have no pelagic forage fishes. Slimy sculpins (Cottus cognatus) are a prey of lake trout and the soft sediment chironomids are an important prey for the sculpin. Our previous work showed that the median size of lake trout in Toolik Lake had decreased significantly between 1977 and 1986, and smaller lake trout are likely to be less effective as sculpin predators. Using our historic data on the slimy sculpin population from 1978, we took advantage of the recent change in the predator community to examine for subsequent changes in the sculpin community. Between 1978 and 1987, the percentage of slimy sculpin caught in the soft sediments has increased (25% to 39.5%). In 1987 there was a significant difference in the mean weight of sculpin caught on different substrates. The mean individual weight of sculpins increased from the nearshore rock area to the rock/soft-sediment interface to the soft sediments. There was no difference in mean individual weight with habitat in 1978. The mean total length at age for slimy sculpins during this time has also increased significantly. We suggest that the risk of predation while foraging in the soft sediments has declined. The increased use of the soft sediment area appears to have contributed to their increased growth, likely due to greater food abundance.