Mechanisms were investigated by which kelp canopies influence abundances of understorey species. First, the amount of shade afforded by kelp canopies and the frequency of scouring by kelp plants of various sizes were quantified. Next, the effects on understorey assemblages due to the reduction of light levels by kelp canopies were determined by manipulating the degree of shading in certain areas and comparing these with unmanipulated controls. Effects due to scouring by kelp laminae were determined by stopping scour in certain areas and comparing these with unmanipuiated controls. Several treatn~ents were included in these experiments to assess artifacts caused by the manipulations. Most species whose abundances changed after removing kelp (i.e. increases in filamentous and turfing algae, decreases in encrusting algae and ascidians), did not change in clearings where artificial shade was supplied. Scour by kelp plants showed no effects on most species, although the amount of sediment and microscopic silt were enhanced by stopping scour, as perhaps were the ahundances of an anemone and an entoprocl. The usefulness of field manipulations to test alternative hypotheses accounting for patterns detected in kelp communities is noted.

Cryptic, not readily detectable, components of fishing mortality are not routinely accounted for in fisheries management because of a lack of adequate data, and for some components, a lack of accurate estimation methods. Cryptic fishing mortalities can cause adverse ecological effects, are a source of wastage, reduce the sustainability of fishery resources and, when unaccounted for, can cause errors in stock assessments and population models. Sources of cryptic fishing mortality are (1) pre-catch losses, where catch dies from the fishing operation but is not brought onboard when the gear is retrieved, (2) ghost-fishing mortality by fishing gear that was abandoned, lost or discarded, (3) post-release mortality of catch that is retrieved and then released alive but later dies as a result of stress and injury sustained from the fishing interaction, (4) collateral mortalities indirectly caused by various ecological effects of fishing and (5) losses due to synergistic effects of multiple interacting sources of stress and injury from fishing operations, or from cumulative stress and injury caused by repeated sub-lethal interactions with fishing operations. To fill a gap in international guidance on best practices, causes and methods for estimating each component of cryptic fishing mortality are described, and considerations for their effective application are identified. Research priorities to fill gaps in understanding the causes and estimating cryptic mortality are highlighted.

Physical disturbances leading to clearances of kelp canopies were investigated for their effects on understorey species. First, frequencies and types of natural dsturbances in a kelp forest were quanhf~ed from data on s t o m activity and undenvater surveys. Storms removed parts of kelp plants, whole plants and groups of plants. The latter led to cleanngs and Increased the quanhty of light reachlng the substratum. Second, manipulative experiments throughout l yr determined temporal vanation in the effects of canopy removal on the understorey assemblage. Replicate areas in the kelp forest were cleared and others left as controls. The microscopic assemblage of species was sampled as well as macroscopic plants and anlmals On substrata cleared in spring, summer and autumn, turf dominated after initial increases in the covers of microalgae and microinvertebrates This turf inhibited kelp recrmtment during dense recruitment in wlnter and persisted for up to 2 yr, unhl kelps encroached into clearings from the edges. In areas cleared d u~i n g dense kelp recruitment (in winter), kelp colonized the substratum together with filamentous and turf algae. The kelp quickly developed a canopy, leadlng to the decline of turf species. These results demonstrate inhibitoqr successions: kelp canopies and areas of turf both occupied the substratum and inhibited the establishmcnt of the other. The type of vegetation found in any place at any hme depended on the timing of, and bme since, the last removal of kelp.

Physical disturbances in a sublittoral kelp community were investigated for their roles in structuring benthc assemblages. Effects of storms that lead to partial and/or complete denudation of kelp plants were investigated in a series of manipulative field experiments. Effects on understorey specles due to differential damage to kelp plants were examined by sampling replicate plots of treatments that imitated the various kinds of damage to kelps. Partial damage to kelp canopies led to similar effects on species to complete removal of kelps, because damaged plants invariably died. Encrusting algae and sponges decreased in cover in manipulated areas while microalgae and then brown turfing species increased in cover. Consequences of living on the borders of clearings in the kelp forest were investigated. Understorey assemblages here contained abundances of both those species found under the kelp canopy and those in the centres of clearings. Effects on understorey species due to thinning the kelp canopy to various densities was investigated. Thnning kelp canopies had similar effects for most species as complete removal of canopies. Fluctuations in abundances of certain species required the removal of at least 50 % of the kelp canopy. Effects on colonizing species of providing clean primary substrata under kelp canopies (as when kelp holdfasts are detached) were investigated. The identity of the various micro-algae that colonized areas of bare substrata under the canopy showed marked variabhty among replicate sites. Results illustrated several complex influences that physical disturbances have on the structure of a kelp community, and ~ndicate the need for comprehensive experimental studies of the effects of physical, disturbances.

Since humans began fishing (at least 90 000 years ago), fishing technology has developed with the objective of trying to catch the greatest quantities of fish possible, of an ever‐increasing variety. Fishing technology has evolved from simple harpoons and hooks to the industrial factory trawlers of the 20th century. After millennia of assuming that seafood resources are inexhaustible, and centuries of somewhat muted concerns that advanced fishing technologies may have detrimental impacts on stocks and ecosystems, the last century has seen advances in fishing technology blamed as a major cause of the current over‐exploitation of fish stocks. It has mainly been during the last few decades that fishing technologists have begun to focus on more conservation‐orientated goals. This occurred initially in response to concerns over the by‐catch of charismatic species (like dolphins in tuna purse‐seines), but quickly broadened to address concerns over the discarding of not‐so‐charismatic species (like juvenile fish killed by shrimp trawling). To ameliorate these issues, technologists and commercial fishers successfully developed various innovative gear‐based and operational solutions. The steps involved in successfully reducing by‐catches have tended to follow a certain incremental framework involving identification of problems using observer programmes, developing technological solution to these problems, experimentally testing these solutions, implementing these solutions throughout industry and finally gaining acceptance of the solutions from concerned interest groups. Most recently public concern has broadened once again from by‐catch issues to encompass a much wider context involving the impacts of fishing on entire ecosystems, i.e. the impacts of fishing on all species affected – not just those species caught, retained or discarded. As a consequence, there have been many calls for ecosystem‐based fisheries management to ensure that fisheries operate under the principles of ecologically sustainable development. Scientists are gradually filling the gaps in our knowledge about how fishing affects whole ecosystems but, because of the scales and complexities involved, such studies are usually difficult, expensive and of long duration. While this descriptive work is difficult, finding solutions to any identified problem is an even greater challenge, particularly for fishing technologists. The easiest solutions to such problems involve rather draconian management strategies like closures. A less extreme alternative involves the development of new technologies that reduce the impacts of fishing on ecosystems – in a similar way as that done to reduce by‐catch problems. Innovations like altering ground‐chains, footropes, sweeps and trawl doors have been suggested as possible ways to ameliorate the environmental damage done by trawling, but such research is still very much in its infancy. Nevertheless, the recent history of fishing technology is chequered with successfully meeting such challenges, giving one confidence...