The genesis and achievement of a limnologist: George Evelyn Hutchinson, 1903-1991

An obituary of the limnologist G.E. Hutchinson is given.

The kingdom of the shore: achievement of good ecological potential in reservoirs

The European Water Framework Directive requires member states to restore aquatic habitats to good ecological status (quality) by 2015. Good ecological status is defined as slightly different from high status, which, according to the Directive, means negligible human influence. This poses problems enough for restoration of natural habitats but artificial reservoirs are not excluded from the Directive. They must be restored to good ecological potential. The meaning of good ecological status is linked to that of 'high' ecological status, the pristine reference condition for aquatic habitats under the Directive. From the point of view of an ecologist, this is taken to mean the presence of four fundamental characteristics: nutrient parsimony, characteristic biological and physical structure, connectivity within a wider system and adequate size to give resilience of the biological communities to environmental change. These characteristics are strongly interrelated. Ecological potential must bear some relationship to ecological status but since the reference state for ecological quality is near absence of human impact, it is difficult to see how the criteria for ecological status can be applied to a completely man-made entity where the purpose of the dam is deliberately to interfere with the natural characteristics of a river or former natural lake. Rservoirs are disabled lakes, ususally lakcing the diversity and function provided by a littoral zone. Nonetheless, pragmatic approaches to increasing the biodiversity of reservours are reviewed and conclusions drawn as to the likely effectivemess of the legislation.

Indirect validation of the age-reading method for Pacific cod (Gadus macrocephalus) using otoliths from marked and recaptured fish

Two examples of indirect validation are described for age-reading methods of Pacific cod (Gadus macrocephalus). Aging criteria that exclude faint translucent zones (checks) in counts of annuli and criteria that include faint zones were both tested. Otoliths from marked and recaptured fish were used to back-calculate the length of each fish at the time of its release by using measurements of the area of annuli. Estimated fish size at time of release and actual observed fish size were similar, supporting the assumption that translucent zones are laid down on an annual basis. A second method for validating reading criteria used otolith age and von Bertalanffy parameters, estimated from the tagging data, to predict how much each fish grew in length after tagging. We found that otolith aging criteria applied to otoliths from tagged and recovered Pacific cod predicted quite accurately the growth increments that we observed in these specimens. These results provide further evidence that the current aging criteria are not underestimating the age of the fish and support our current interpretation of checks (i.e., as subannual marks). We expect these indirect validations to advance age determination for Pacific cod, which in turn would enhance development of stock assessment methods based on age structure for this species in the eastern Bering Sea.

River Dart Scale Reading Investigation Report on the 1965 Season

This is the fourth River Dart Scale Reading Investigation Report on the 1965 season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All it summarized in tables, and figures are included plotting weight distributions for each age classes and frequency distributions.

River Dart Scale Reading Investigation Report on the 1966 Season

This is the fifth River Dart Scale Reading Investigation Report on the 1966 Season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All it summarized in tables, and figures are included plotting weight distributions for each age classes and frequency distributions. It also compares the results of previous reports.

River Dart Scale Reading Investigation Report on the 1967 Season

This is the sixth and final River Dart Scale Reading Investigation Report on the 1967 Season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All it summarized in tables, and figures are included plotting weight distributions for each age classes and frequency distributions. It also compares the results of previous reports and gives a full summary for the investigation (including previous reports).

River Dart Scale Reading Investigation Report on the 1962 Season

This is the first River Dart Scale Reading Investigation Report on the 1962 season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. It reviews briefly the theory and mechanics of the scale-reading technique, the life history of the salmon, and the methods used for the collection of scales and the examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All are summarized in various tables and figures are also included, plotting weight distributions for each age classes and frequency distributions.

River Dart Scale Reading Investigation Report on the 1963 Season

This is the second River Dart Scale Reading Investigation Report on the 1963 season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All are summarized in tables, and figures are alo included plotting weight distributions for each age classes and frequency distributions. The report also remarks the similarity of the results with those for 1962.

River Dart Scale Reading Investigation Report on the 1964 Season

This is the third River Dart Scale Reading Investigation Report on the 1964 season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All are summarized in tables, and figures are also included plotting weight distributions for each age classes and frequency distributions. After three years of the investigation a pattern is emerging which shows that the Dart salmon population is mainly composed of four year old fish, which have spent two years in the river and then two year or little longer at sea.

River Dart Scale Reading Investigation 1971

This is the River Dart Scale Reading Investigation Report on the 1971 season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. In 1967 the final report on a five-year scale reading programme was summarised, at the time it was considered sufficient information to help with restocking programmes and the management of salmon population. But a further scale reading programme was started in an attempt to monitor changing patterns in salmon runs that may be caused by the new influences. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All are summarized in tables, and figures are also included plotting weight distributions for each age classes and frequency distributions.

River Dart Scale Reading Investigation 1972

This is the River Dart Scale Reading Investigation Report on the 1972 season by the Devon River Board. The object of this investigation is to examine, by means of scale-reading, the general biology of the salmon population of the River Dart. In 1967 the final report on a five-year scale reading programme was summarised, at the time it was considered sufficient information to help with restocking programmes and the management of salmon population. But a further scale reading programme was started in an attempt to monitor changing patterns in salmon runs that may be caused by the new influences. It reviews the methods used for collection of the scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All is summarized in tables, and figures are included showing weight distributions for each age classes and frequency distributions.

River Exe Scale Reading Investigation. 5th Annual Report for the 1970 Season

This is the 5th Annual Report of the Rive Exe Scale Reading Investigation for the 1970 season by the Devon River Authority. The object of this investigation is to examine, by means of scale reading, the biology of age classes of the salmon population of the River Exe. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All is summarized in tables, and figures are included showing weight distributions for each age classes and frequency distributions.

River Exe Scale Reading Investigation. 6th Annual Report for the 1971 Season.

This is the 6th Annual Report of the Rive Exe Scale Reading Investigation for the 1971 Season by the Devon River Authority. The object of this investigation is to examine, by means of scale reading, the biology of age classes of the salmon population of the River Exe. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All is summarized in tables, and figures are included showing weight distributions for each age classes and frequency distributions.

River Exe Scale Reading Investigation. 7th Annual Report for the 1972 season

This is the 7th Annual Report of the Rive Exe Scale Reading Investigation for the 1972 Season by the Devon River Authority. The object of this investigation is to examine, by means of scale reading, the biology of age classes of the salmon population of the River Exe. It reviews the methods used for the collection of scales and examination of the materials. It shows the results of the survey and the number of scales studied from each of the various sea-age classes, time of running with distribution of the sea-age groups throughout the season, fish sizes and smolt ages at migration. All is summarized in tables, and figures are included showing weight distributions for each age classes and frequency distributions.

Salmon Scale Reading Investigation 1972

This is the Salmon Scale Reading Investigation from 1972 by Cornwall River Authority. The object of this investigation is to examine, by means of scale reading, the biology of age classes of the salmon populations of the River Tamar, River Tavy, River Lynher, River Fowey, River Camel and River Plym. It contains for each river the numbers of caught salmon, number of scales received and which were unreadable and percentages in each age group separately for net and rod caught. Length and weight frequency distribution histograms have been plotted to show the size distribution of the various sea age group.