Preliminary phytoplankton counts in the Sanyati Basin, Lake Kariba

Phytoplankton counts were made on a monthly basis on water samples, taken from one station in the Sanyati Basin. The results show seasonal fluctuations which are probably nutrient dependant. High phytoplankton numbers occur at times of high nutrient levels as was found with the crustacean zooplankton populations (Marshall 1980). Numbers also decreased with depth down to the thermocline. Below the thermocline there was little or no change in numbers.

A coarse fish close season on canals. Paper in evidence to the review of fisheries policy and legislation. Paper number: EA-12

This paper gives the results of the Environment Agency's research into the canal close season to the Salmon and Freshwater Fisheries Review Group. It presents the findings of the research, explains why the research was undertaken and how it relates to the Agency's duties. The background for this report includes that angling representative bodies have long argued that the existing situation in which somecanals have a close season and others do not, is unsatisfactory.

Precision estimates and suggested sample sizes for length-frequency data

For most fisheries applications, the shape of a length-frequency distribution is much more important than its mean length or variance. This makes it difficult to evaluate at which point a sample size is adequate. By estimating the coefficient of variation of the counts in each length class and taking a weighted mean of these, a measure of precision was obtained that takes the precision in all length classes into account. The precision estimates were closely associated with the ratio of the sample size to the number of size classes in each sample. As a rule-of-thumb, a minimum sample size of 10 times the number of length classes in the sample is suggested because the precision deteriorates rapidly for smaller sample sizes. In absence of such a rule-of-thumb, samplers have previously under-estimated the required sample size for samples with large fish, while over-sampling small fish of the same species.

Effect of type of otolith and preparation technique on age estimation of larval and juvenile spot (Leiostomus xanthurus)

Otoliths of larval and juvenile fish provide a record of age, size, growth, and development (Campana and Neilson, 1985; Thorrold and Hare, 2002). However, determining the time of first increment formation in otoliths (Campana, 2001) and assessing the accuracy (deviation from real age) and precision (repeatability of increment counts from the same otolith) of increment counts are prerequisites for using otoliths to study the life history of fish (Campana and Moksness, 1991). For most fish species, first increment deposition occurs either at hatching, a day after hatching, or after first feeding and yolksac absorption (Jones, 1986; Thorrold and Hare, 2002). Increment deposition before hatching also occurs (Barkmann and Beck, 1976; Radtke and Dean, 1982). If first increment deposition does not occur at hatching, the standard procedure is to add a predetermined number to increment counts to estimate fish age (Campana and Neilson, 1985).

Beluga, Delphinapterus leucas, Group Sizes in Cook Inlet, Alaska, Based on Observer Counts and Aerial Video

Belugas, Delphinapterus leucas, groups were videotaped concurrent to observer counts during annual NMFS aerial surveys of Cook Inlet, Alaska, from 1994 to 2000. The videotapes provided permanent records of whale groups that could be examined and compared to group size estimates ade by aerial observers.Examination of the video recordings resulted in 275 counts of 79 whale groups. The McLaren formula was used to account for whales missed while they were underwater (average correction factor 2.03; SD=0.64). A correction for whales missed due to video resolution was developed by using a second, paired video camera that magnified images relative to the standard video. This analysis showed that some whales were missed either because their image size fell below the resolution of hte standard video recording or because two whales surfaced so close to each other that their images appeared to be one large whale. The correction method that resulted depended on knowing the average whale image size in the videotapes. Image sizes were measured for 2,775 whales from 275 different passes over whale groups. Corrected group sizes were calcualted as the product of the original count from video, the correction factor for whales missed underwater, and the correction factor for whales missed due to video resolution (averaged 1.17; SD=0.06). A regression formula was developed to estimate group sizes from aerial observer counts; independent variables were the aerial counts and an interaction term relative to encounter rate (whales per second during the counting of a group), which were regressed against the respective group sizes as calculated from the videotapes. Significant effects of encounter rate, either positive or negative, were found for several observers. This formula was used to estimate group size when video was not available. The estimated group sizes were used in the annual abundance estimates.

Restormel Annual Report 2001

This is the Restormel Fish Counter, Annual Report 2001 produced by the Environment Agency South West Region on March 2002. The report presents the daily upstream counts of migratory salmonids on the River Fowey at Restormel Weir fish counting station (SX 107 613) in 2001. The counter data covers the period of the commercial salmonid net buy back scheme and the national spring salmon byelaws. These reduce the commercial netting season for salmon and sea trout to between 16 June and 31 August. The fish counter at Restormel is installed on a crump sectioned weir on the River Fowey. The fish counter is a resistivity based system and operates over all three channels of the weir. 2001 was a good year for large sea trout. The number of returning large sea trout was above average in April, May, June and July and equal to or higher than the previous recorded maximum in those months. The main run of small sea trout occurred at a similar time to previous years with the highest numbers of fish entering the Fowey during June and July.

Gunnislake Fish Counter Annual Report 2002

This is the Gunnislake Fish Counter Annual Report 2002 from the Environment Agency South West Region, which was held on March 2002. It presents the daily upstream counts of migratory salmonids recorded on the River Tamar at Gunnislake Weir fish counting station in 2002. The data within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Bylaws. The report contains section on Net Buy-Back; Species Apportionment; Validation of counter efficiency; results as total number of migratory salmonid (salmon and Sea Trout) counted moving upstream in 2002 at Gunnislake; video validation and Counter Efficiency; and Discussion. The section Discussion includes Salmon and Sea Trout counts recorded on the River Tamar 1995-2002, other fish species observed as sea lamprey and Environmental Factors (river flows, water temperature, and barometric pressure).

Restormel Fish Counter Annual Report 2006

This is the Restormel Fish Counter, Annual Report 2006 produced by the Environment Agency South West Region on March 2007. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel weir fish counting station (SX 107 613) over the period March 2006 to February 2007 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws (2 March- 15 June inclusive). The minimum upstream salmon estimate for 2005 (1046), over the period July 2005 to February 2006, was 20% lower than that recorded over the same period in 2004 (1301). However, this is the second highest count recorded over the past 11 years. The total sea trout count (10448) was 8% higher than 2004 (9608). The number of salmon and large sea trout was lower than average in 2005. However, the overall numbers of adult salmon and sea trout returning have been increasing year on year since 1997. This overall increase in the salmon and sea trout counts, together with the consistency of the numbers of fish returning over recent years suggests that measures designed to protect salmonid stocks in the River Fowey are working.

Restormel Fish Counter Annual Report 2007

This is the Restormel Fish Counter, Annual Report 2007 produced by the Environment Agency South West Region on March 2008. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2007 to February 2008 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws (2 March- 15 June). The minimum upstream salmon estimate for 2007, over the period July 2007 to February 2008, was 796, which is the fifth highest recorded count over the past 13 years. The number of returning salmon in 2007 suggests a downward trend in numbers since 2004. The 2007 large sea trout count is similar to 2006. Overall, the number of fish returning is still low in comparison with the 10-year average. There was a noticeable decrease in the number of small sea trout returning compared to 2006 and the 10-year average. The Fish counter at Restormel suffered several faults.

Restormel Fish Counter Annual Report 2008

This is the Restormel Fish Counter, Annual Report 2008 produced by the Environment Agency South West Region on April 2009. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2008 to February 2009 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws. The minimum upstream salmon estimate for 2008, over the period July 2008 to February 2009, was 938 and is the third highest recorded count over the past 14 years. The 2008 large sea trout count (482) shows a marked improvement in the number of returning fish when compared to 2007 (241). There was a significant decrease in the number of small sea trout returning in 2008 when compared to 2007 and the 10-year average.

Restormel Fish Counter Annual Report 2008

This is the Restormel Fish Counter, Annual Report 2008 produced by the Environment Agency South West Region on April 2009. The report presents the upstream counts of migratory salmonids recorded on the River Fowey at Restormel Weir fish counting station (SX 107 613) over the period March 2008 to February 2009 inclusive. Data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the National Spring Salmon Byelaws. The minimum upstream salmon estimate for 2008, over the period July 2008 to February 2009, was 938, which is the third highest recorded count over the past 14 years. The 2008 large sea trout count (482) shows a marked improvement in the number of returning fish when compared to 2007 (241). There was a significant decrease in the number of small sea trout returning in 2008 when compared to 2007 and the 10-year average. The fish counter suffered several faults equated to 12.5 days during this period.

Larval development and identification of the genus Triglops (Scorpaeniformes: Cottidae)

Prior to Pietsch’s (1993) revision of the genus Triglops, identification of their larvae was difficult; six species co-occur in the eastern North Pacific Ocean and Bering Sea and three co-occur in the western North Atlantic Ocean. We examined larvae from collections of the Alaska Fisheries Science Center and Atlantic Reference Centre and used updated meristic data, pigment patterns, and morphological characters to identify larvae of Triglops forficatus, T. macellus, T. murrayi, T. nybelini, T. pingeli, and T. scepticus; larvae of T. metopias, T. dorothy, T. jordani, and T. xenostethus have yet to be identified and are thus not included in this paper. Larval Triglops are characterized by a high myomere count (42–54), heavy dorsolateral pigmentation on the gut, and a pointed snout. Among species co-occurring in the eastern North Pacific Ocean, T. forficatus, T. macellus, and T. pingeli larvae are distinguished from each other by meristic counts and presence or absence of a series of postanal ventral melanophores. Triglops scepticus is differentiated from other eastern North Pacific Ocean larvae by having 0–3 postanal ventral melanophores, a large eye, and a large body depth. Among species co-occurring in the western North Atlantic Ocean, T. murrayi and T. pingeli larvae are distinguished from each other by meristic counts (vertebrae, dorsal-fin rays, and anal-fin rays once formed), number of postanal ventral melanophores, and first appearance and size of head spines. Triglops nybelini is distinguished from T. murrayi and T. pingeli by a large eye, pigment on the lateral line and dorsal midline in flexion larvae, and a greater number of dorsal-fin rays and pectoral-fin rays once formed.

Use of skeletochronological analysis to estimate the age of leatherback sea turtles Dermochelys coriacea in the western North Atlantic

Although growth rate and age data are essential for leatherback management, estimates of these demographic parameters remain speculative due to the cryptic life history of this endangered species. Skeletochronological analysis of scleral ossicles obtained from 8 captive, known-age and 33 wild leatherbacks originating from the western North Atlantic was conducted to characterize the ossicles and the growth marks within them. Ages were accurately estimated for the known-age turtles, and their growth mark attributes were used to calibrate growth mark counts for the ossicles from wild specimens. Due to growth mark compaction and resorption, the number of marks visible at ossicle section tips was consistently and significantly greater than the number visible along the lateral edges, demonstrating that growth mark counts should be performed at the tips so that age is not underestimated. A correction factor protocol that incorporated the trajectory of early growth increments was used to estimate the number of missing marks in those ossicles exhibiting resorption, which was then added to the number of observed marks to obtain an age estimate for each turtle. A generalized smoothing spline model, von Bertalanffy growth curve, and size-at-age function were used to obtain estimates of age at maturity for leatherbacks in the western North Atlantic. Results of these analyses suggest that median age at maturation for leatherbacks in this part of the world may range from 24.5 to 29 yr. These age estimates are much greater than those proposed in previous studies and have significant implications for population management and recovery.

Trends in counts of manatees Trichechus manatus latirostris from 1987 to 2006 in waters of Sarasota County, Florida, USA

To demonstrate the utility of distributional surveys for assessing relative abundance and trends in counts for a discrete area of coastline, aerial survey data from Sarasota County, Florida, USA, were analyzed for the years 1987 to 2006. The study area was divided into 3 regions: the Sarasota Bay Region (SBR; N = 353 surveys), Lemon Bay (N = 368), and the Myakka River (N = 209). Manatee counts varied significantly across seasons (p < 0.0001) for all 3 regions. Manatees within Sarasota County utilized open bays primarily in the warmer months. Such usage may have been influenced by resource availability. Conversely, usage of the Myakka River peaked in winter months when manatees seek warm-water refugia such as Warm Mineral Spring. Marginal means for yearly counts within Lemon Bay and the SBR increased significantly, beginning midway through the survey period (1996) until the early 2000s. In contrast, mean yearly counts within the Myakka River decreased over this time period. After record lows in 2003 for Lemon Bay and the Myakka River, and a considerable decline in 2004 for the SBR, mean yearly counts for all 3 regions showed an increasing trend over the remaining 2 yr of the study. Greater protection of manatee habitat and availability of forage coincided with the increase in numbers of manatees using Sarasota County waters during the 1990s, and the subsequent decline in numbers may be indicative of the increase in mortality in recent years due to watercraft collisions and severe red tide events.